CVS update: php3/doc/chapters

From:	jim	Date:	Fri, 28 May 1999 22:22:22 +0000
Subject:	CVS update: php3/doc/chapters
Groups:	php.dev
Request:	Send a blank email to php-dev+get-6214@lists.php.net to get a copy of this message

Date: Friday May 28, 1999 @ 18:22 Author: jim Update of /repository/php3/doc/chapters In directory php:/tmp/cvs-serv20136/chapters Modified Files: intro.sgml lang-syntax.sgml Removed Files: lang-const.sgml Log Message: A bunch more reorganization, some new text, and general progress towards making the 'Language Reference' part of the manual useful. Still in progress, but getting closer. Index: php3/doc/chapters/intro.sgml diff -u php3/doc/chapters/intro.sgml:1.13 php3/doc/chapters/intro.sgml:1.14 --- php3/doc/chapters/intro.sgml:1.13 Tue May 25 01:11:44 1999 +++ php3/doc/chapters/intro.sgml Fri May 28 18:22:22 1999 @@ -7,15 +7,50 @@ <simpara> PHP is a server-side HTML-embedded scripting language. + <para> + Simple answer, but what does that mean? An example: + <example> + <title>An introductory example</title> + <programlisting> +<html><head><title>Example</title> +<body> +<?php echo "Hi, I'm a PHP script!"; ?> +</body></html> + </programlisting> + </example> + + <para> + Notice how this is different from a CGI script written in other + languages like Perl or C -- instead of writing a program with lots + of commands to output HTML, you write an HTML script with a some + embedded code to do something (in this case, output some text). The + PHP code is enclosed in special start and end tags that allow you + to jump into and out of "PHP mode". + + <para> + What distinguishes PHP from something like client-side Javascript + is that the code is executed on the server. If you were to have a + script similar to the above on your server, the client would receive + the results of running that script, with no way of determining what + the underlying code may be. You can even configure your web server + to process all your HTML files with PHP, and then there's really no + way that users can tell what you have up your sleeve. + <sect1 id="intro-whatcando"> <title>What can PHP do?</title> + <para> - Perhaps the strongest and most significant feature in PHP3 is its - database integration layer. Writing a database-enabled web page - is incredibly simple. The following databases are currently + At the most basic level, PHP can do anything any other CGI + program can do, such as collect form data, generate dynamic + page content, or send and receive cookies. + + <para> + Perhaps the strongest and most significant feature in PHP is its + support for a wide range of databases. Writing a database-enabled + web page is incredibly simple. The following databases are currently supported: <blockquote> - <simplelist columns=2> + <simplelist columns=3> <member>Adabas D</member> <member>dBase</member> <member>Empress</member> @@ -33,17 +68,10 @@ </simplelist> </blockquote> - - - + <para> + PHP also has support for talking to other services using protocols + such as IMAP, SNMP, NNTP, POP3, or even HTTP. You can even open raw + network sockets and interact using other protocols. <sect1 id="intro-history"> <title>A Brief History of PHP</title> @@ -61,7 +89,7 @@ the Personal Home Page tools scripts with the Form Interpreter and added mSQL support and PHP/FI was born. PHP/FI grew at an amazing pace and people started contributing code to it. - </simpara> + <simpara> It is hard to give any hard statistics, but it is estimated that by late 1996 PHP/FI was in use on at least 15,000 web sites around @@ -73,15 +101,21 @@ and this new parser formed the basis for PHP Version 3. A lot of the utility code from PHP/FI was ported over to PHP3 and a lot of it was completely rewritten. - </simpara> + <simpara> - Today (mid-1998) either PHP/FI or PHP3 ships with a number of + Today (mid-1999) either PHP/FI or PHP3 ships with a number of commercial products such as C2's StrongHold web server and RedHat Linux and a conservative estimate based on an extrapolation from - numbers provided by NetCraft would be that PHP is in use on 150,000 - sites around the world. To put that in perspective, that is more - sites than run Netscape's flagship Enterprise server on the Internet. - </simpara> + numbers provided by NetCraft would be that PHP is in use on over + 150,000 sites around the world. To put that in perspective, that + is more sites than run Netscape's flagship Enterprise server on + the Internet. + + <simpara> + Also as of this writing, work is underway on the next generation of + PHP that will utilize the powerful Zend scripting engine to deliver + higher performance, and will also support running under webservers + other than Apache as a native server module. </chapter> Index: php3/doc/chapters/lang-syntax.sgml diff -u php3/doc/chapters/lang-syntax.sgml:1.42 php3/doc/chapters/lang-syntax.sgml:1.43 --- php3/doc/chapters/lang-syntax.sgml:1.42 Tue May 25 01:11:44 1999 +++ php3/doc/chapters/lang-syntax.sgml Fri May 28 18:22:22 1999 @@ -5,70 +5,73 @@ PHP's syntax is borrowed primarily from C. Java and Perl have also influenced the syntax. - <sect1 id="syntax-phpmode"> - <title>Escaping from HTML</title> + <sect1 id="basic-syntax"> + <title>Basic Syntax</title> + + <sect2 id="basic-syntax.phpmode"> + <title>Escaping from HTML</title> - <para> - There are four ways of escaping from HTML and entering "PHP code - mode": + <para> + There are four ways of escaping from HTML and entering "PHP code + mode": - <para> - <example> - <title>Ways of escaping from HTML</title> - <programlisting> + <para> + <example> + <title>Ways of escaping from HTML</title> + <programlisting> 1. <? echo ("this is the simplest, an SGML processing instruction\n"); ?> - + 2. <?php echo("if you want to serve XML documents, do like this\n"); ?> 3. <script language="php"> echo ("some editors (like FrontPage) don't - like processing instructions"); + like processing instructions"); </script> 4. <% echo ("As of PHP 3.0.4 you may optionally use ASP-style tags"); %> <%= $variable; # This is a shortcut for "<%echo .." %> - </programlisting> - </example> + </programlisting> + </example> - <para> - The first way is only available if short tags have been enabled - (either by calling <function>short_tags</function>, they are - configured on using the short_tags run-time configuration setting, - or they are enabled using the --enable-short-tags compile-time - configuration setting. + <para> + The first way is only available if short tags have been enabled + (either by calling <function>short_tags</function>, they are + configured on using the short_tags run-time configuration setting, + or they are enabled using the --enable-short-tags compile-time + configuration setting. - <para> - The fourth way is only available if ASP-style tags have been - enabled using either the asp_tags configuration setting or the - --enable-asp-tags compile-time configuration setting. + <para> + The fourth way is only available if ASP-style tags have been + enabled using either the asp_tags configuration setting or the + --enable-asp-tags compile-time configuration setting. - <para> - The closing "bracket" for the block will include the immediately - trailing newline if one is present. + <para> + The closing "bracket" for the block will include the immediately + trailing newline if one is present. - <sect1 id="syntax-instrsep"> - <title>Instruction separation</title> + <sect2 id="basic-syntax.instruction-separation"> + <title>Instruction separation</title> - <simpara> - Instructions are separated the same as in C or perl - terminate - each statement with a semicolon. + <simpara> + Instructions are separated the same as in C or perl - terminate + each statement with a semicolon. - <para> - The closing tag (?>) also implies the end of the statement, so the - following are equivalent: + <para> + The closing tag (?>) also implies the end of the statement, so the + following are equivalent: - <informalexample> - <programlisting> + <informalexample> + <programlisting> <?php echo "This is a test"; ?> <?php echo "This is a test" ?> - </programlisting> - </informalexample> + </programlisting> + </informalexample> - <sect1 id="comment-syntax"> - <title>Commenting code</title> + <sect2 id="basic-syntax.comments"> + <title>Comments</title> <para> PHP supports 'C', 'C++' and Unix shell-style comments. For example: @@ -90,7 +93,7 @@ comes first. <informalexample><programlisting> <h1>This is an <?# echo "simple";?> example.</h1> -<p>The header above will says 'This is an example'. +<p>The header above will say 'This is an example'. </programlisting></informalexample> <simpara> @@ -134,7 +137,7 @@ Note that a variable may behave in different manners in certain situations, depending on what type it is a the time. For more information, see the section on <link - linkend="variable-typejuggling">Type Juggling</link>. + linkend="variables.type-juggling">Type Juggling</link>. <sect2 id="types.integer"> <title>Integers</title> @@ -366,209 +369,22 @@ $bar -> do_foo (); </programlisting> </informalexample> - - <sect1 id="expressions"> - <title>Expressions</title> - - <simpara> - Expressions are the most important building stones of PHP. In PHP, - almost anything you write is an expression. The simplest yet - most accurate way to define an expressions is "anything that has a - value". - - <simpara> - The most basic forms of expressions are constants and variables. - When you type "$a = 5", you're assigning '5' into $a. '5', obviously, - has the value 5, or in other words '5' is an expression with the - value of 5 (in this case, '5' is an integer constant). - - <simpara> - After this assignment, you'd expect $a's value to be 5 as - well, so if you wrote $b = $a, you'd expect it to behave just as - if you wrote $b = 5. In other words, $a is an expression with the - value of 5 as well. If everything works right, this is exactly - what will happen. - - <para> - Slightly more complex examples for expressions are functions. For - instance, consider the following function: - - <informalexample> - <programlisting> -function foo () { - return 5; -} - </programlisting> - </informalexample> - - <simpara> - Assuming you're familiar with the concept of functions (if you're - not, take a look at the chapter about functions), you'd assume - that typing <literal>$c = foo()</literal> is essentially just like - writing <literal>$c = 5</literal>, and you're right. Functions - are expressions with the value of their return value. Since foo() - returns 5, the value of the expression 'foo()' is 5. Usually - functions don't just return a static value but compute something. - - <simpara> - Of course, values in PHP don't have to be integers, and very often - they aren't. PHP supports three scalar value types: integer values, - floating point values and string values (scalar values are values that - you can't 'break' into smaller pieces, unlike arrays, for instance). - PHP also supports two composite (non-scalar) types: arrays and - objects. Each of these value types can be assigned into variables or - returned from functions. - - <simpara> - So far, users of PHP/FI 2 shouldn't feel any change. However, PHP - takes expressions much further, in the same way many other - languages do. PHP is an expression-oriented language, in the - sense that almost everything is an expression. Consider the - example we've already dealt with, '$a = 5'. It's easy to see that - there are two values involved here, the value of the integer - constant '5', and the value of $a which is being updated to 5 as - well. But the truth is that there's one additional value involved - here, and that's the value of the assignment itself. The - assignment itself evaluates to the assigned value, in this case 5. - In practice, it means that '$a = 5', regardless of what it does, - is an expression with the value 5. Thus, writing something like - '$b = ($a = 5)' is like writing '$a = 5; $b = 5;' (a semicolon - marks the end of a statement). Since assignments are parsed in a - right to left order, you can also write '$b = $a = 5'. - - <simpara> - Another good example of expression orientation is pre- and - post-increment and decrement. Users of PHP/FI 2 and many other - languages may be familiar with the notation of variable++ and - variable--. These are increment and decrement operators. In - PHP/FI 2, the statement '$a++' has no value (is not an - expression), and thus you can't assign it or use it in any way. - PHP enhances the increment/decrement capabilities by making - these expressions as well, like in C. In PHP, like in C, there - are two types of increment - pre-increment and post-increment. - Both pre-increment and post-increment essentially increment the - variable, and the effect on the variable is idential. The - difference is with the value of the increment expression. - Pre-increment, which is written '++$variable', evaluates to the - incremented value (PHP increments the variable before reading its - value, thus the name 'pre-increment'). Post-increment, which is - written '$variable++' evaluates to the original value of - $variable, before it was incremented (PHP increments the variable - after reading its value, thus the name 'post-increment'). - - <simpara> - A very common type of expressions are comparison expressions. - These expressions evaluate to either 0 or 1, meaning FALSE or TRUE - (respectively). PHP supports > (bigger than), >= (bigger than or - equal to), == (equal), < (smaller than) and <= (smaller than or - equal to). These expressions are most commonly used inside - conditional execution, such as IF statements. - - <simpara> - The last example of expressions we'll deal with here is combined - operator-assignment expressions. You already know that if you - want to increment $a by 1, you can simply write '$a++' or '++$a'. - But what if you want to add more than one to it, for instance 3? - You could write '$a++' multiple times, but this is obviously not a - very efficient or comfortable way. A much more common practice is - to write '$a = $a + 3'. '$a + 3' evaluates to the value of $a - plus 3, and is assigned back into $a, which results in - incrementing $a by 3. In PHP, as in several other languages - like C, you can write this in a shorter way, which with time would - become clearer and quicker to understand as well. Adding 3 to the - current value of $a can be written '$a += 3'. This means exactly - "take the value of $a, add 3 to it, and assign it back into $a". - In addition to being shorter and clearer, this also results in - faster execution. The value of '$a += 3', like the value of a - regular assignment, is the assigned value. Notice that it is NOT - 3, but the combined value of $a plus 3 (this is the value that's - assigned into $a). Any two-place operator can be used in this - operator-assignment mode, for example '$a -= 5' (subtract 5 from - the value of $a), '$b *= 7' (multiply the value of $b by 7), etc. - - <para> - There is one more expression that may seem odd if you haven't seen - it in other languages, the ternary conditional operator: - - <informalexample><programlisting> -$first ? $second : $third -</programlisting></informalexample> - - If the value of the first subexpression is true (non-zero), then - it the second subexpression is evaluated, and that is the result - of the conditional expression. Otherwise, the third subexpression - is evaluated, and that is the value. - - <para> - The following example should help you understand pre- and - post-increment and expressions in general a bit better: - - <informalexample> - <programlisting> -function double($i) { - return $i*2; -} -$b = $a = 5; /* assign the value five into the variable $a and $b */ -$c = $a++; /* post-increment, assign original value of $a - (5) to $c */ -$e = $d = ++$b; /* pre-increment, assign the incremented value of - $b (6) to $d and $e */ - -/* at this point, both $d and $e are equal to 6 */ - -$f = double($d++); /* assign twice the value of $d <emphasis>before</emphasis> - the increment, 2*6 = 12 to $f */ -$g = double(++$e); /* assign twice the value of $e <emphasis>after</emphasis> - the increment, 2*7 = 14 to $g */ -$h = $g += 10; /* first, $g is incremented by 10 and ends with the - value of 24. the value of the assignment (24) is - then assigned into $h, and $h ends with the value - of 24 as well. */ -</programlisting></informalexample> - - <simpara> - In the beginning of the chapter we said that we'll be describing - the various statement types, and as promised, expressions can be - statements. However, not every expression is a statement. In - this case, a statement has the form of 'expr' ';' that is, an - expression followed by a semicolon. In '$b=$a=5;', $a=5 is a - valid expression, but it's not a statement by itself. '$b=$a=5;' - however is a valid statement. - - <simpara> - One last thing worth mentioning is the truth value of expressions. - In many events, mainly in conditional execution and loops, you're - not interested in the specific value of the expression, but only - care about whether it means TRUE or FALSE (PHP doesn't have a - dedicated boolean type). The truth value of expressions in PHP is - calculated in a similar way to perl. Any numeric non-zero numeric - value is TRUE, zero is FALSE. Be sure to note that negative - values are non-zero and are thus considered TRUE! The empty - string and the string "0" are FALSE; all other strings are TRUE. - With non-scalar values (arrays and objects) - if the value - contains no elements it's considered FALSE, otherwise it's - considered TRUE. - <simpara> - PHP provides a full and powerful implementation of expressions, and - documenting it entirely goes beyond the scope of this manual. The - above examples should give you a good idea about what expressions - are and how you can construct useful expressions. Throughout the - rest of this manual we'll write 'expr' to indicate any valid PHP - expression. + <sect1 id="variables"> + <title>Variables</title> - <sect1 id="variable-scope"> - <title>Variable scope</title> + <sect2 id="variables.scope"> + <title>Variable scope</title> - <simpara> - The scope of a variable is the context within which it is defined. - For the most part all PHP variables only have a single scope. - However, within user-defined functions a local function scope is - introduced. Any variable used inside a function is by default - limited to the local function scope. For example: + <simpara> + The scope of a variable is the context within which it is defined. + For the most part all PHP variables only have a single scope. + However, within user-defined functions a local function scope is + introduced. Any variable used inside a function is by default + limited to the local function scope. For example: - <informalexample> - <programlisting> + <informalexample> + <programlisting> $a = 1; /* global scope */ Function Test () { @@ -576,22 +392,22 @@ } Test (); - </programlisting> - </informalexample> + </programlisting> + </informalexample> - <simpara> - This script will not produce any output because the echo statement - refers to a local version of the $a variable, and it has not been - assigned a value within this scope. You may notice that this is a - little bit different from the C language in that global variables - in C are automatically available to functions unless specifically - overridden by a local definition. This can cause some problems in - that people may inadvertently change a global variable. In PHP - global variables must be declared global inside a function if they - are going to be used in that function. An example: + <simpara> + This script will not produce any output because the echo statement + refers to a local version of the $a variable, and it has not been + assigned a value within this scope. You may notice that this is a + little bit different from the C language in that global variables + in C are automatically available to functions unless specifically + overridden by a local definition. This can cause some problems in + that people may inadvertently change a global variable. In PHP + global variables must be declared global inside a function if they + are going to be used in that function. An example: - <informalexample> - <programlisting> + <informalexample> + <programlisting> $a = 1; $b = 2; @@ -603,22 +419,22 @@ Sum (); echo $b; - </programlisting> - </informalexample> + </programlisting> + </informalexample> - <simpara> - The above script will output "3". By declaring $a and - $b global within the function, all references to either variable - will refer to the global version. There is no limit to the number - of global variables that can be manipulated by a function. + <simpara> + The above script will output "3". By declaring $a and + $b global within the function, all references to either variable + will refer to the global version. There is no limit to the number + of global variables that can be manipulated by a function. - <simpara> - A second way to access variables from the global scope is to use - the special PHP-defined $GLOBALS array. The previous example can - be rewritten as: + <simpara> + A second way to access variables from the global scope is to use + the special PHP-defined $GLOBALS array. The previous example can + be rewritten as: - <informalexample> - <programlisting> + <informalexample> + <programlisting> $a = 1; $b = 2; @@ -628,63 +444,63 @@ Sum (); echo $b; - </programlisting> - </informalexample> + </programlisting> + </informalexample> - <simpara> - The $GLOBALS array is an associative array with the name of the - global variable being the key and the contents of that variable - being the value of the array element. + <simpara> + The $GLOBALS array is an associative array with the name of the + global variable being the key and the contents of that variable + being the value of the array element. - <simpara> - Another important feature of variable scoping is the - <emphasis>static</emphasis> variable. A static variable exists - only in a local function scope, but it does not lose its value - when program execution leaves this scope. Consider the following - example: + <simpara> + Another important feature of variable scoping is the + <emphasis>static</emphasis> variable. A static variable exists + only in a local function scope, but it does not lose its value + when program execution leaves this scope. Consider the following + example: - <informalexample> - <programlisting> + <informalexample> + <programlisting> Function Test () { $a = 0; echo $a; $a++; } - </programlisting> - </informalexample> + </programlisting> + </informalexample> - <simpara> - This function is quite useless since every time it is called it - sets $a to 0 and prints "0". The $a++ which increments - the variable serves no purpose since as soon as the function exits - the $a variable disappears. To make a useful counting function - which will not lose track of the current count, the $a variable is - declared static: + <simpara> + This function is quite useless since every time it is called it + sets $a to 0 and prints "0". The $a++ which increments + the variable serves no purpose since as soon as the function exits + the $a variable disappears. To make a useful counting function + which will not lose track of the current count, the $a variable is + declared static: - <informalexample> - <programlisting> + <informalexample> + <programlisting> Function Test () { static $a = 0; echo $a; $a++; } - </programlisting> - </informalexample> + </programlisting> + </informalexample> - <simpara> - Now, every time the Test() function is called it will print the - value of $a and increment it. + <simpara> + Now, every time the Test() function is called it will print the + value of $a and increment it. - <simpara> - Static variables are also essential when functions are called - recursively. A recursive function is one which calls itself. - Care must be taken when writing a recursive function because it is - possible to make it recurse indefinitely. You must make sure you - have an adequate way of terminating the recursion. The following - simple function recursively counts to 10: + <simpara> + Static variables are also essential when functions are called + recursively. A recursive function is one which calls itself. + Care must be taken when writing a recursive function because it is + possible to make it recurse indefinitely. You must make sure you + have an adequate way of terminating the recursion. The following + simple function recursively counts to 10: - <informalexample> - <programlisting> + <informalexample> + <programlisting> Function Test () { static $count = 0; @@ -695,105 +511,103 @@ } $count--; } - </programlisting> - </informalexample> + </programlisting> + </informalexample> - <sect1 id="variable-variable"> - <title>Variable variables</title> + <sect2 id="variables.variable"> + <title>Variable variables</title> - <simpara> - Sometimes it is convenient to be able to have variable variable - names. That is, a variable name which can be set and used - dynamically. A normal variable is set with a statement such as: + <simpara> + Sometimes it is convenient to be able to have variable variable + names. That is, a variable name which can be set and used + dynamically. A normal variable is set with a statement such as: - <informalexample> - <programlisting> + <informalexample> + <programlisting> $a = "hello"; - </programlisting> - </informalexample> + </programlisting> + </informalexample> - <simpara> - A variable variable takes the value of a variable and treats that as the - name of a variable. In the above example, <emphasis>hello</emphasis>, can - be used as the name of a variable by using two dollar signs. ie. + <simpara> + A variable variable takes the value of a variable and treats that as the + name of a variable. In the above example, <emphasis>hello</emphasis>, can + be used as the name of a variable by using two dollar signs. ie. - <informalexample> - <programlisting> + <informalexample> + <programlisting> $$a = "world"; - </programlisting> - </informalexample> + </programlisting> + </informalexample> - <simpara> - At this point two variables have been defined and stored in the - PHP symbol tree: $a with contents "hello" and $hello with contents - "world". Therefore, this statement: + <simpara> + At this point two variables have been defined and stored in the + PHP symbol tree: $a with contents "hello" and $hello with contents + "world". Therefore, this statement: - <informalexample> - <programlisting> + <informalexample> + <programlisting> echo "$a ${$a}"; - </programlisting> - </informalexample> + </programlisting> + </informalexample> - <simpara> - produces the exact same output as: + <simpara> + produces the exact same output as: - <informalexample> - <programlisting> + <informalexample> + <programlisting> echo "$a $hello"; - </programlisting> - </informalexample> - - <simpara> - ie. they both produce: <emphasis>hello world</emphasis>. + </programlisting> + </informalexample> - <simpara> - In order to use variable variables with arrays, you have to - resolve an ambiguity problem. That is, if you write $$a[1] then - the parser needs to know if you meant to use $a[1] as a variable, - or if you wanted $$a as the variable and then the [1] index from - that variable. The syntax for resolving this ambiguity is: - ${$a[1]} for the first case and ${$a}[1] for the second. + <simpara> + ie. they both produce: <emphasis>hello world</emphasis>. + <simpara> + In order to use variable variables with arrays, you have to + resolve an ambiguity problem. That is, if you write $$a[1] then + the parser needs to know if you meant to use $a[1] as a variable, + or if you wanted $$a as the variable and then the [1] index from + that variable. The syntax for resolving this ambiguity is: + ${$a[1]} for the first case and ${$a}[1] for the second. - <sect1 id="variable-external"> - <title>Variables from outside PHP</title> - <simpara></simpara> + <sect2 id="variables.external"> + <title>Variables from outside PHP</title> - <sect2> - <title>HTML Forms (GET and POST)</title> + <sect3 id="variables.external.form"> + <title>HTML Forms (GET and POST)</title> - <simpara> - When a form is submitted to a PHP script, any variables from that - form will be automatically made available to the script by - PHP. For instance, consider the following form: + <simpara> + When a form is submitted to a PHP script, any variables from that + form will be automatically made available to the script by + PHP. For instance, consider the following form: - <para> - <example> - <title>Simple form variable</title> - <programlisting> + <para> + <example> + <title>Simple form variable</title> + <programlisting> <form action="foo.php3" method="post"> Name: <input type="text" name="name"><br> <input type="submit"> </form> - </programlisting> - </example> + </programlisting> + </example> - <simpara> - When submitted, PHP will create the variable - <computeroutput>$name</computeroutput>, which will will contain - whatever what entered into the <emphasis>Name:</emphasis> field - on the form. + <simpara> + When submitted, PHP will create the variable + <computeroutput>$name</computeroutput>, which will will contain + whatever what entered into the <emphasis>Name:</emphasis> field + on the form. - <simpara> - PHP also understands arrays in the context of form variables, but - only in one dimension. You may, for example, group related - variables together, or use this feature to retrieve values from a - multiple select input: + <simpara> + PHP also understands arrays in the context of form variables, but + only in one dimension. You may, for example, group related + variables together, or use this feature to retrieve values from a + multiple select input: - <para> - <example> - <title>More complex form variables</title> - <programlisting> + <para> + <example> + <title>More complex form variables</title> + <programlisting> <form action="array.html" method="post"> Name: <input type="text" name="personal[name]"><br> Email: <input type="text" name="personal[email]"><br> @@ -804,29 +618,29 @@ </select> <input type="submit"> </form> - </programlisting> - </example> + </programlisting> + </example> - <simpara> - If PHP's track_vars feature is turned on, either by the <link - linkend="ini.track-vars">track_vars</link> configuration setting - or the <computeroutput><?php_track_vars?></computeroutput> - directive, then variables submitted via the POST or GET methods - will also be found in the global associative arrays - $HTTP_POST_VARS and $HTTP_GET_VARS as appropriate. + <simpara> + If PHP's track_vars feature is turned on, either by the <link + linkend="ini.track-vars">track_vars</link> configuration setting + or the <computeroutput><?php_track_vars?></computeroutput> + directive, then variables submitted via the POST or GET methods + will also be found in the global associative arrays + $HTTP_POST_VARS and $HTTP_GET_VARS as appropriate. - <sect3> - <title>IMAGE SUBMIT variable names</TITLE> + <sect4> + <title>IMAGE SUBMIT variable names</TITLE> <simpara> When submitting a form, it is possible to use an image instead of the standard submit button with a tag like: - <informalexample> - <programlisting> + <informalexample> + <programlisting> <input type=image src="image.gif" name="sub"> - </programlisting> - </informalexample> + </programlisting> + </informalexample> <simpara> When the user clicks somewhere on the image, the accompanying @@ -836,10 +650,9 @@ the actual variable names sent by the browser contains a period rather than an underscore, but PHP converts the period to an underscore automatically. - - <sect2> - <title>HTTP Cookies</title> + <sect3 id="variables.external.cookies"> + <title>HTTP Cookies</title> <simpara> PHP transparently supports HTTP cookies as defined by <ulink @@ -852,63 +665,56 @@ restriction as for the <function>Header</function> function. Any cookies sent to you from the client will automatically be turned into a PHP variable just like GET and POST method data. - </simpara> <simpara> If you wish to assign multiple values to a single cookie, just add <emphasis>[]</emphasis> to the cookie name. For example: - <informalexample> - <programlisting> + <informalexample> + <programlisting> SetCookie ("MyCookie[]", "Testing", time()+3600); - </programlisting> - </informalexample> + </programlisting> + </informalexample> - <simpara> - Note that a cookie will replace a previous cookie by the same - name in your browser unless the path or domain is different. So, - for a shopping cart application you may want to keep a counter - and pass this along. i.e. + <simpara> + Note that a cookie will replace a previous cookie by the same + name in your browser unless the path or domain is different. So, + for a shopping cart application you may want to keep a counter + and pass this along. i.e. - <example> - <title>SetCookie Example</title> - <programlisting> + <example> + <title>SetCookie Example</title> + <programlisting> $Count++; SetCookie ("Count", $Count, time()+3600); SetCookie ("Cart[$Count]", $item, time()+3600); - </programlisting> - </example> - + </programlisting> + </example> - <sect2> - <title>Environment variables</title> + <sect3 id="variables.external.environment"> + <title>Environment variables</title> - <para> - PHP automatically makes environment variables available as normal - PHP variables. + <para> + PHP automatically makes environment variables available as normal + PHP variables. <informalexample> <programlisting> echo $HOME; /* Shows the HOME environment variable, if set. */ </programlisting> </informalexample> - - <para> - Since information coming in via GET, POST and Cookie mechanisms - also automatically create PHP variables, it is sometimes best to - explicitly read a variable from the environment in order to make - sure that you are getting the right version. The - <function>getenv</function> function can be used for this. You - can also set an environment variable with the - <function>putenv</function> function. - - <sect2> - <title>Server configuration directives</title> - <simpara></simpara> + <para> + Since information coming in via GET, POST and Cookie mechanisms + also automatically create PHP variables, it is sometimes best to + explicitly read a variable from the environment in order to make + sure that you are getting the right version. The + <function>getenv</function> function can be used for this. You + can also set an environment variable with the + <function>putenv</function> function. - <sect1 id="variable-typejuggling"> - <title>Type juggling</title> + <sect2 id="variables.type-juggling"> + <title>Type juggling</title> <simpara> PHP does not require (or support) explicit type definition in @@ -942,6 +748,7 @@ <simpara> If the last two examples above seem odd, see <link linkend="lang-syntax.stringconv">String conversion</link>. + <simpara> If you wish to force a variable to be evaluated as a certain type, see the section on <link @@ -949,21 +756,21 @@ wish to change the type of a variable, see <function>settype</function>. - <sect2> - <title>Determining variable types</title> + <sect3> + <title>Determining variable types</title> - <para> - Because PHP determines the types of variables and converts them - (generally) as needed, it is not always obvious what type a given - variable is at any one time. PHP includes several functions - which find out what type a variable is. They are - <function>gettype</function>, <function>is_long</function>, - <function>is_double</function>, <function>is_string</function>, - <function>is_array</function>, and - <function>is_object</function>. + <para> + Because PHP determines the types of variables and converts them + (generally) as needed, it is not always obvious what type a given + variable is at any one time. PHP includes several functions + which find out what type a variable is. They are + <function>gettype</function>, <function>is_long</function>, + <function>is_double</function>, <function>is_string</function>, + <function>is_array</function>, and + <function>is_object</function>. - <sect2 id="lang-syntax.typecasting"> - <title>Type casting</title> + <sect3 id="lang-syntax.typecasting"> + <title>Type casting</title> <para> Type casting in PHP works much as it does in C: the name of the @@ -998,9 +805,9 @@ </programlisting> </informalexample> + <sect3 id="lang-syntax.stringconv"> + <title>String conversion</title> - <sect2 id="lang-syntax.stringconv"> - <title>String conversion</title> <simpara> When a string is evaluated as a numeric value, the resulting value and type are determined as follows. @@ -1039,22 +846,1753 @@ <simpara> For more information on this conversion, see the Unix manual page for strtod(3). + </sect1> - </chapter> + <sect1 id="constants"> + <title>Constants</title> - + <simpara> + PHP defines several constants and provides a mechanism for defining + more at run-time. Constants are much like variables, save for the two + facts that constants must be defined using the + <function>define</function> function, and that they cannot later + be redefined to another value. + + <para> + The predefined constants (always available) are: + + <variablelist> + + <varlistentry> + <term>__FILE__</term> + <listitem> + <simpara> + The name of the script file presently being parsed. If used + within a file which has been included or required, then the + name of the included file is given, and not the name of the + parent file. + </simpara> + </listitem> + </varlistentry> + + <varlistentry> + <term>__LINE__</term> + <listitem> + <simpara> + The number of the line within the current script file which is + being parsed. If used within a file which has been included or + required, then the position within the included file is given. + </simpara> + </listitem> + </varlistentry> + + <varlistentry> + <term>PHP_VERSION</term> + <listitem> + <simpara> + The string representation of the version of the PHP parser + presently in use; e.g. '3.0.8-dev'. + </simpara> + </listitem> + </varlistentry> + + <varlistentry> + <term>PHP_OS</term> + <listitem> + <simpara> + The name of the operating system on which the PHP parser is + executing; e.g. 'Linux'. + </simpara> + </listitem> + </varlistentry> + + <varlistentry> + <term>TRUE</term> + <listitem> + <simpara> + A true value. + </simpara> + </listitem> + </varlistentry> + + <varlistentry> + <term>FALSE</term> + <listitem> + <simpara> + A false value. + </simpara> + </listitem> + </varlistentry> + + <varlistentry> + <term>E_ERROR</term> + <listitem> + <simpara> + Denotes an error other than a parsing error from which + recovery is not possible. + </simpara> + </listitem> + </varlistentry> + + <varlistentry> + <term>E_WARNING</term> + <listitem> + <simpara> + Denotes a condition where PHP knows something is wrong, but + will continue anyway; these can be caught by the script + itself. An example would be an invalid regexp in + <function>ereg</function>. + </simpara> + </listitem> + </varlistentry> + + <varlistentry> + <term>E_PARSE</term> + <listitem> + <simpara> + The parser choked on invalid syntax in the script + file. Recovery is not possible. + </simpara> + </listitem> + </varlistentry> + + <varlistentry> + <term>E_NOTICE</term> + <listitem> + <simpara> + Something happened which may or may not be an error. Execution + continues. Examples include using an unquoted string as a + hash index, or accessing a variable which has not been set. + </simpara> + </listitem> + </varlistentry> + </variablelist> + + <para> + The E_* constants are typically used with the + <function>error_reporting</function> function for setting the + error reporting level. + + <para> + You can define additional constants using the + <function>define</function> function. + + <para> + Note that these are constants, not C-style macros; only valid + scalar data may be represented by a constant. + + <example> + <title>Defining Constants</title> + <programlisting> +<?php +define("CONSTANT", "Hello world."); +echo CONSTANT; // outputs "Hello world." +?> + </programlisting> + </example> + + <example> + <title>Using __FILE__ and __LINE__</title> + <programlisting> +<?php +function report_error($file, $line, $message) { + echo "An error occured in $file on line $line: $message."; +} + +report_error(__FILE__,__LINE__, "Something went wrong!"); +?> + </programlisting> + </example> + </sect1> + + <sect1 id="expressions"> + <title>Expressions</title> + + <simpara> + Expressions are the most important building stones of PHP. In PHP, + almost anything you write is an expression. The simplest yet + most accurate way to define an expressions is "anything that has a + value". + + <simpara> + The most basic forms of expressions are constants and variables. + When you type "$a = 5", you're assigning '5' into $a. '5', obviously, + has the value 5, or in other words '5' is an expression with the + value of 5 (in this case, '5' is an integer constant). + + <simpara> + After this assignment, you'd expect $a's value to be 5 as + well, so if you wrote $b = $a, you'd expect it to behave just as + if you wrote $b = 5. In other words, $a is an expression with the + value of 5 as well. If everything works right, this is exactly + what will happen. + + <para> + Slightly more complex examples for expressions are functions. For + instance, consider the following function: + + <informalexample> + <programlisting> +function foo () { + return 5; +} + </programlisting> + </informalexample> + + <simpara> + Assuming you're familiar with the concept of functions (if you're + not, take a look at the chapter about functions), you'd assume + that typing <literal>$c = foo()</literal> is essentially just like + writing <literal>$c = 5</literal>, and you're right. Functions + are expressions with the value of their return value. Since foo() + returns 5, the value of the expression 'foo()' is 5. Usually + functions don't just return a static value but compute something. + + <simpara> + Of course, values in PHP don't have to be integers, and very often + they aren't. PHP supports three scalar value types: integer values, + floating point values and string values (scalar values are values that + you can't 'break' into smaller pieces, unlike arrays, for instance). + PHP also supports two composite (non-scalar) types: arrays and + objects. Each of these value types can be assigned into variables or + returned from functions. + + <simpara> + So far, users of PHP/FI 2 shouldn't feel any change. However, PHP + takes expressions much further, in the same way many other + languages do. PHP is an expression-oriented language, in the + sense that almost everything is an expression. Consider the + example we've already dealt with, '$a = 5'. It's easy to see that + there are two values involved here, the value of the integer + constant '5', and the value of $a which is being updated to 5 as + well. But the truth is that there's one additional value involved + here, and that's the value of the assignment itself. The + assignment itself evaluates to the assigned value, in this case 5. + In practice, it means that '$a = 5', regardless of what it does, + is an expression with the value 5. Thus, writing something like + '$b = ($a = 5)' is like writing '$a = 5; $b = 5;' (a semicolon + marks the end of a statement). Since assignments are parsed in a + right to left order, you can also write '$b = $a = 5'. + + <simpara> + Another good example of expression orientation is pre- and + post-increment and decrement. Users of PHP/FI 2 and many other + languages may be familiar with the notation of variable++ and + variable--. These are increment and decrement operators. In + PHP/FI 2, the statement '$a++' has no value (is not an + expression), and thus you can't assign it or use it in any way. + PHP enhances the increment/decrement capabilities by making + these expressions as well, like in C. In PHP, like in C, there + are two types of increment - pre-increment and post-increment. + Both pre-increment and post-increment essentially increment the + variable, and the effect on the variable is idential. The + difference is with the value of the increment expression. + Pre-increment, which is written '++$variable', evaluates to the + incremented value (PHP increments the variable before reading its + value, thus the name 'pre-increment'). Post-increment, which is + written '$variable++' evaluates to the original value of + $variable, before it was incremented (PHP increments the variable + after reading its value, thus the name 'post-increment'). + + <simpara> + A very common type of expressions are comparison expressions. + These expressions evaluate to either 0 or 1, meaning FALSE or TRUE + (respectively). PHP supports > (bigger than), >= (bigger than or + equal to), == (equal), < (smaller than) and <= (smaller than or + equal to). These expressions are most commonly used inside + conditional execution, such as IF statements. + + <simpara> + The last example of expressions we'll deal with here is combined + operator-assignment expressions. You already know that if you + want to increment $a by 1, you can simply write '$a++' or '++$a'. + But what if you want to add more than one to it, for instance 3? + You could write '$a++' multiple times, but this is obviously not a + very efficient or comfortable way. A much more common practice is + to write '$a = $a + 3'. '$a + 3' evaluates to the value of $a + plus 3, and is assigned back into $a, which results in + incrementing $a by 3. In PHP, as in several other languages + like C, you can write this in a shorter way, which with time would + become clearer and quicker to understand as well. Adding 3 to the + current value of $a can be written '$a += 3'. This means exactly + "take the value of $a, add 3 to it, and assign it back into $a". + In addition to being shorter and clearer, this also results in + faster execution. The value of '$a += 3', like the value of a + regular assignment, is the assigned value. Notice that it is NOT + 3, but the combined value of $a plus 3 (this is the value that's + assigned into $a). Any two-place operator can be used in this + operator-assignment mode, for example '$a -= 5' (subtract 5 from + the value of $a), '$b *= 7' (multiply the value of $b by 7), etc. + + <para> + There is one more expression that may seem odd if you haven't seen + it in other languages, the ternary conditional operator: + + <informalexample><programlisting> +$first ? $second : $third +</programlisting></informalexample> + + If the value of the first subexpression is true (non-zero), then + it the second subexpression is evaluated, and that is the result + of the conditional expression. Otherwise, the third subexpression + is evaluated, and that is the value. + + <para> + The following example should help you understand pre- and + post-increment and expressions in general a bit better: + + <informalexample> + <programlisting> +function double($i) { + return $i*2; +} +$b = $a = 5; /* assign the value five into the variable $a and $b */ +$c = $a++; /* post-increment, assign original value of $a + (5) to $c */ +$e = $d = ++$b; /* pre-increment, assign the incremented value of + $b (6) to $d and $e */ + +/* at this point, both $d and $e are equal to 6 */ + +$f = double($d++); /* assign twice the value of $d <emphasis>before</emphasis> + the increment, 2*6 = 12 to $f */ +$g = double(++$e); /* assign twice the value of $e <emphasis>after</emphasis> + the increment, 2*7 = 14 to $g */ +$h = $g += 10; /* first, $g is incremented by 10 and ends with the + value of 24. the value of the assignment (24) is + then assigned into $h, and $h ends with the value + of 24 as well. */ +</programlisting></informalexample> + + <simpara> + In the beginning of the chapter we said that we'll be describing + the various statement types, and as promised, expressions can be + statements. However, not every expression is a statement. In + this case, a statement has the form of 'expr' ';' that is, an + expression followed by a semicolon. In '$b=$a=5;', $a=5 is a + valid expression, but it's not a statement by itself. '$b=$a=5;' + however is a valid statement. + + <simpara> + One last thing worth mentioning is the truth value of expressions. + In many events, mainly in conditional execution and loops, you're + not interested in the specific value of the expression, but only + care about whether it means TRUE or FALSE (PHP doesn't have a + dedicated boolean type). The truth value of expressions in PHP is + calculated in a similar way to perl. Any numeric non-zero numeric + value is TRUE, zero is FALSE. Be sure to note that negative + values are non-zero and are thus considered TRUE! The empty + string and the string "0" are FALSE; all other strings are TRUE. + With non-scalar values (arrays and objects) - if the value + contains no elements it's considered FALSE, otherwise it's + considered TRUE. + + <simpara> + PHP provides a full and powerful implementation of expressions, and + documenting it entirely goes beyond the scope of this manual. The + above examples should give you a good idea about what expressions + are and how you can construct useful expressions. Throughout the + rest of this manual we'll write <replaceable>expr</replaceable> + to indicate any valid PHP expression. + + <sect1 id="operators"> + <title>Operators</title> + <simpara> + </simpara> + + <sect2 id="arithmetic-operators"> + <title>Arithmetic Operators</title> + <simpara> + Remember basic arithmetic from school? These work just + like those. + </simpara> + + <table> + <title>Arithmetic Operators</title> + <tgroup cols="3"> + <thead> + <row> + <entry>example</entry> + <entry>name</entry> + <entry>result</entry> + </row> + </thead> + <tbody> + <row> + <entry>$a + $b</entry> + <entry>Addition</entry> + <entry>Sum of $a and $b.</entry> + </row> + <row> + <entry>$a - $b</entry> + <entry>Subtraction</entry> + <entry>Remainder of $b subtracted from $a.</entry> + </row> + <row> + <entry>$a * $b</entry> + <entry>Multiplication</entry> + <entry>Product of $a and $b.</entry> + </row> + <row> + <entry>$a / $b</entry> + <entry>Division</entry> + <entry>Dividend of $a and $b.</entry> + </row> + <row> + <entry>$a % $b</entry> + <entry>Modulus</entry> + <entry>Remainder of $a divided by $b.</entry> + </row> + </tbody> + </tgroup> + </table> + + + + <sect2 id="string-operators"> + <title>String Operators</title> + <simpara> + There is only really one string operator -- the concatenation + operator ("."). + </simpara> + <para> + <informalexample><programlisting> +$a = "Hello "; +$b = $a . "World!"; // now $b = "Hello World!" + </programlisting></informalexample> + </para> + + <sect2 id="assignment-operators"> + <title>Assignment Operators</title> + <simpara> + The basic assignment operator is "=". Your first inclination might + be to think of this as "equal to". Don't. It really means that + the the left operand gets set to the value of the expression on the + rights (that is, "gets set to"). + </simpara> + <para> + The value of an assignment expression is the value assigned. That + is, the value of "$a = 3" is 3. This allows you to do some tricky + things: <informalexample><programlisting> +$a = ($b = 4) + 5; // $a is equal to 9 now, and $b has been set to 4. +</programlisting></informalexample> + </para> + <para> + In addition to the basic assignment operator, there are "combined + operators" for all of the binary arithmetic and string operators + that allow you to use a value in an expression and then set its + value to the result of that expression. For example: <informalexample><programlisting> +$a = 3; +$a += 5; // sets $a to 8, as if we had said: $a = $a + 5; +$b = "Hello "; +$b .= "There!"; // sets $b to "Hello There!", just like $b = $b . "There!"; +</programlisting></informalexample> + </para> + + <sect2 id="bitwise-operators"> + <title>Bitwise Operators</title> + <simpara> + Bitwise operators allow you to turn specific bits within an integer + on or off. + </simpara> + + <table> + <title>Bitwise Operators</title> + <tgroup cols="3"> + <thead> + <row> + <entry>example</entry> + <entry>name</entry> + <entry>result</entry> + </row> + </thead> + <tbody> + <row> + <entry>$a & $b</entry> + <entry>And</entry> + <entry>Bits that are set in both $a and $b are set.</entry> + </row> + <row> + <entry>$a | $b</entry> + <entry>Or</entry> + <entry>Bits that are set in either $a or $b are set.</entry> + </row> + <row> + <entry>~ $a</entry> + <entry>Not</entry> + <entry>Bits that are set in $a are not set, and vice versa.</entry> + </row> + <row> + <entry>$a << $b</entry> + <entry>Shift left</entry> + <entry>Shift the bits of $a $b steps to the left (each step means "multiply by two")</entry> + </row> + <row> + <entry>$a >> $b</entry> + <entry>Shift right</entry> + <entry>Shift the bits of $a $b steps to the right (each step means "divide by two")</entry> + </row> + </tbody> + </tgroup> + </table> + + <sect2 id="logical-operators"> + <title>Logical Operators</title> + + <table> + <title>Logical Operators</title> + <tgroup cols="3"> + <thead> + <row> + <entry>example</entry> + <entry>name</entry> + <entry>result</entry> + </row> + </thead> + <tbody> + <row> + <entry>$a and $b</entry> + <entry>And</entry> + <entry>True of both $a and $b are true.</entry> + </row> + <row> + <entry>$a or $b</entry> + <entry>Or</entry> + <entry>True if either $a or $b is true.</entry> + </row> + <row> + <entry>$a xor $b</entry> + <entry>Or</entry> + <entry>True if either $a or $b is true, but not both.</entry> + </row> + <row> + <entry>! $a</entry> + <entry>Not</entry> + <entry>True if $a is not true.</entry> + </row> + <row> + <entry>$a && $b</entry> + <entry>And</entry> + <entry>True of both $a and $b are true.</entry> + </row> + <row> + <entry>$a || $b</entry> + <entry>Or</entry> + <entry>True if either $a or $b is true.</entry> + </row> + </tbody> + </tgroup> + </table> + + <simpara> + The reason for the two different variations of "and" and "or" + operators is that they operate at different precedences. (See below.) + </simpara> + + <sect2 id="comparison-operators"> + <title>Comparison Operators</title> + <simpara> + Comparison operators, as their name imply, allow you to compare two + values. + </simpara> + + <table> + <title>Comparson Operators</title> + <tgroup cols="3"> + <thead> + <row> + <entry>example</entry> + <entry>name</entry> + <entry>result</entry> + </row> + </thead> + <tbody> + <row> + <entry>$a == $b</entry> + <entry>Equal</entry> + <entry>True if $a is equal to $b.</entry> + </row> + <row> + <entry>$a != $b</entry> + <entry>Not equal</entry> + <entry>True if $a is not equal to $b.</entry> + </row> + <row> + <entry>$a < $b</entry> + <entry>Less than</entry> + <entry>True if $a is strictly less than $b.</entry> + </row> + <row> + <entry>$a > $b</entry> + <entry>Greater than</entry> + <entry>True if $a is strictly greater than $b.</entry> + </row> + <row> + <entry>$a <= $b</entry> + <entry>Less than or equal to </entry> + <entry>True if $a is less than or equal to $b.</entry> + </row> + <row> + <entry>$a >= $b</entry> + <entry>Greater than or equal to </entry> + <entry>True if $a is greater than or equal to $b.</entry> + </row> + </tbody> + </tgroup> + </table> + + <para> + Another conditional operator is the "?:" (or trinary) operator, which + operates as in C and many other languages. + <informalexample><programlisting>(expr1) ? (expr2) : (expr3);</programlisting></informalexample> + This expression returns to <replaceable>expr2</replaceable> if + <replaceable>expr1</replaceable> evalutes to true, and expr3 if + <replaceable>expr1</replaceable> evaluates to false. + + <sect2 id="precedence"> + <title>Operator Precedence</title> + <para> + The precedence of an operator specifies how "tightly" it binds + two expressions together. For example, in the expression + <literal>1 + 5 * 3</literal>, the answer is 16 and not + 18 because the multiplication ("*") operator has a higher precedence + than the addition ("+") operator. + <para> + The following table lists the precedence of operators with the + lowest-precedence operators listed first. + + <table> + <title>Operator Precedence</title> + <tgroup cols="2"> + <thead> + <row> + <entry>Associativity</entry> + <entry>Operators</entry> + </row> + </thead> + <tbody> + <row> + <entry>left</entry> + <entry>,</entry> + </row> + <row> + <entry>left</entry> + <entry>or</entry> + </row> + <row> + <entry>left</entry> + <entry>xor</entry> + </row> + <row> + <entry>left</entry> + <entry>and</entry> + </row> + <row> + <entry>right</entry> + <entry>print</entry> + </row> + <row> + <entry>left</entry> + <entry>= += -= *= /= .= %= &= != ~= <<= >>=</entry> + </row> + <row> + <entry>left</entry> + <entry>? :</entry> + </row> + <row> + <entry>left</entry> + <entry>||</entry> + </row> + <row> + <entry>left</entry> + <entry>&&</entry> + </row> + <row> + <entry>left</entry> + <entry>|</entry> + </row> + <row> + <entry>left</entry> + <entry>^</entry> + </row> + <row> + <entry>left</entry> + <entry>&</entry> + </row> + <row> + <entry>non-associative</entry> + <entry>== !=</entry> + </row> + <row> + <entry>non-associative</entry> + <entry>< <= > >=</entry> + </row> + <row> + <entry>left</entry> + <entry><< >></entry> + </row> + <row> + <entry>left</entry> + <entry>+ - .</entry> + </row> + <row> + <entry>left</entry> + <entry>* / %</entry> + </row> + <row> + <entry>right</entry> + <entry>! ~ ++ -- (int) (double) (string) (array) (object) @</entry> + </row> + <row> + <entry>right</entry> + <entry>[</entry> + </row> + <row> + <entry>non-associative</entry> + <entry>new</entry> + </row> + </tbody> + </tgroup> + </table> + + <sect1 id="control-structures"> + <title>Control Structures</title> + <simpara> + Any PHP script is built out of a series of statements. A statement can + be an assignment, a function call, a loop, a conditional statement of + even a statement that does nothing (an empty statement). Statements + usually end with a semicolon. In addition, statements can be grouped + into a statement-group by encapsulating a group of statements with + curly braces. A statement-group is a statement by itself as well. The + various statement types are described in this chapter. + + <sect2 id="construct.if"> + <title><literal>if</literal></title> + + <para> + The <literal>if</literal> construct is one of the most important + features of many languages, PHP included. It allows for conditional + execution of code fragments. PHP features an <literal>if</literal> + structure that is similar to that of C: + + <informalexample><programlisting> + if (expr) + statement + </programlisting></informalexample> + + <simpara> + As described in the section about expressions, expr is evaluated + to its truth value. If <replaceable>expr</replaceable> evaluates + to <literal>TRUE</literal>, PHP will execute statement, and if it + evaluates to <literal>FALSE</literal> - it'll ignore it. + + <para> + The following example would display <computeroutput>a is bigger + than b</computeroutput> if <replaceable>$a</replaceable> is bigger + than <replaceable>$b</replaceable>: + + <informalexample><programlisting> + if ($a > $b) + print "a is bigger than b"; + </programlisting></informalexample> + + <para> + Often you'd want to have more than one statement to be executed + conditionally. Of course, there's no need to wrap each statement + with an <literal>if</literal> clause. Instead, you can group + several statements into a statement group. + For example, this code would display <computeroutput>a is bigger than + b</computeroutput> if <replaceable>$a</replaceable> is bigger than + <replaceable>$b</replaceable>, and would then assign the value of + <replaceable>$a</replaceable> into <replaceable>$b</replaceable>: + + <informalexample><programlisting> + if ($a > $b) { + print "a is bigger than b"; + $b = $a; + } + </programlisting></informalexample> + + <simpara> + If statements can be nested indefinitely within other + <literal>if</literal> statements, which provides you with complete + flexibility for conditional execution of the various parts of + your program. + + </sect2> + + <sect2 id="construct.else"> + <title><literal>else</literal></title> + + <para> + Often you'd want to execute a statement if a certain condition + is met, and a different statement if the condition is not met. + This is what <literal>else</literal> is for. <literal>else</literal> + extends an <literal>if</literal> statement to execute a statement + in case the expression in the <literal>if</literal> statement + evaluates to <literal>FALSE</literal>. For example, the following + code would display <computeroutput>a is bigger than b</computeroutput> + if <replaceable>$a</replaceable> is bigger than <replaceable>$b</replaceable>, + and <computeroutput>a is NOT bigger than b</computeroutput> otherwise: + + <informalexample> + <programlisting> + if ($a > $b) { + print "a is bigger than b"; + } else { + print "a is NOT bigger than b"; + } + </programlisting> + </informalexample> + + The <literal>else</literal> statement is only executed + if the <literal>if</literal> expression evaluated to + <literal>FALSE</literal>, and if there were any <literal>elseif</literal> + expressions - only if they evaluated to <literal>FALSE</literal> + as well (see below). + + <sect2 id="construct.elseif"> + <title><literal>elseif</literal></title> + + <para> + <literal>elseif</literal>, as its name suggests, is a combination + of <literal>if</literal> and <literal>else</literal>. Like + <literal>else</literal>, it extends an <literal>if</literal> + statement to execute a different statement in case the + original <literal>if</literal> expression evaluates to + <literal>FALSE</literal>. However, unlike <literal>else</literal>, + it will execute that alternative expression only if the + <literal>elseif</literal> conditional expression evaluates to + <literal>TRUE</literal>. For example, the following code would + display <computeroutput>a is bigger than b</computeroutput>, + <computeroutput>a equal to b</computeroutput> or <computeroutput>a + is smaller than b</computeroutput>: + + <informalexample> + <programlisting> + if ($a > $b) { + print "a is bigger than b"; + } elseif ($a == $b) { + print "a is equal to b"; + } else { + print "a is smaller than b"; + } + </programlisting> + </informalexample> + + <simpara> + There may be several <literal>elseif</literal>s within the same + <literal>if</literal> statement. The first <literal>elseif</literal> + expression (if any) that evaluates to <literal>true</literal> + would be executed. In PHP, you can also write 'else if' (in two + words) and the behavior would be identical to the one of 'elseif' + (in a single word). The syntactic meaning is slightly different + (if you're familiar with C, this is the same behavior) but the + bottom line is that both would result in exactly the same behavior. + + <simpara> + The <literal>elseif</literal> statement is only executed if the preceding + <literal>if</literal> expression and any + preceding <literal>elseif</literal> expressions evaluated to <literal>FALSE</literal>, and the current + <literal>elseif</literal> expression evaluated to <literal>TRUE</literal>. + + <sect2> + <title>Alternative syntax for <literal>if</literal> structures: <literal>if(): ... endif;</literal></title> + + <para> + PHP offers a different way to group statements within an + <literal>if</literal> statement. This is most commonly used when + you nest HTML blocks inside <literal>if</literal> statements, but + can be used anywhere. Instead of using curly braces, <literal>if + (<replaceable>expr</replaceable>)</literal> should be followed + by a colon, the list of one or more statements, and end with + <literal>endif;</literal>. Consider the following example: + + <informalexample> + <programlisting> + <?php if ($a==5): ?> + A = 5 + <?php endif; ?> + </programlisting> + </informalexample> + + <simpara> + In the above example, the HTML block "A = 5" is nested within an + <literal>if</literal> statement written in the alternative syntax. + The HTML block would be displayed only if $a is equal to 5. + + <para> + The alternative syntax applies to <literal>else</literal> + and <literal>elseif</literal> as well. The following is an + <literal>if</literal> structure with <literal>elseif</literal> + and <literal>else</literal> in the alternative format: + + <informalexample> + <programlisting> + if ($a == 5): + print "a equals 5"; + print "..."; + elseif ($a == 6): + print "a equals 6"; + print "!!!"; + else: + print "a is neither 5 nor 6"; + endif; + </programlisting> + </informalexample> + + <sect2 id="construct.while"> + <title><literal>while</literal></title> + + <para> + <literal>while</literal> loops are the simplest type of loop in PHP. + They behave just like their C counterparts. The basic form of a + <literal>while</literal> statement is: + + <informalexample> + <programlisting> + while (expr) statement + </programlisting> + </informalexample> + + <simpara> + The meaning of a <literal>while</literal> statement is simple. + It tells PHP to execute the nested statement(s) repeatedly, + as long as the <literal>while</literal> expression evaluates + to <literal>TRUE</literal>. The value of the expression is + checked each time at the beginning of the loop, so even if this + value changes during the execution of the nested statement(s), + execution will not stop until the end of the iteration (each + time PHP runs the statements in the loop is one iteration). + Sometimes, if the <literal>while</literal> expression evaluates + to <literal>FALSE</literal> from the very beginning, the nested + statement(s) won't even be run once. + + <para> + Like with the <literal>if</literal> statement, you can group + multiple statements within the same <literal>while</literal> loop + by surrounding a group of statements with curly braces, or by using + the alternate syntax: + + <informalexample> + <programlisting> + while (expr): statement ... endwhile; + </programlisting></informalexample> + + <para> + The following examples are identical, and both print numbers from + 1 to 10: + + <informalexample> + <programlisting> + /* example 1 */ + + $i = 1; + while ($i <= 10) { + print $i++; /* the printed value would be + $i before the increment + (post-increment) */ + } + + /* example 2 */ + + $i = 1; + while ($i <= 10): + print $i; + $i++; + endwhile; + </programlisting> + </informalexample> + + + <sect2 id="construct.do.while"> + <title><literal>do..while</literal></title> + + <simpara> + <literal>do..while</literal> loops are very similar to + <literal>while</literal> loops, except the truth expression is + checked at the end of each iteration instead of in the beginning. + The main difference from regular <literal>while</literal> loops + is that the first iteration of a <literal>do..while</literal> + loop is guarenteed to run (the truth expression is only checked + at the end of the iteration), whereas it's may not necessarily run + with a regular <literal>while</literal> loop (the truth expression + is checked at the beginning of each iteration, if it evaluates + to <literal>FALSE</literal> right from the beginning, the loop + execution would end immediately). + + <para> + There is just one syntax for <literal>do..while</literal> loops: + + <informalexample> + <programlisting> + $i = 0; + do { + print $i; + } while ($i>0); + </programlisting> + </informalexample> + + <simpara> + The above loop would run one time exactly, since after the first + iteration, when truth expression is checked, it evaluates to + <literal>FALSE</literal> ($i is not bigger than 0) and the loop + execution ends. + + <para> + Advanced C users may be familiar with a different usage of + the <literal>do..while</literal> loop, to allow stopping + execution in the middle of code blocks, by encapsulating + them with <literal>do..while</literal>(0), and using the <link + linkend="construct.break"><literal>break</literal></link> statement. + The following code fragment demonstrates this: + + <informalexample> + <programlisting> + do { + if ($i < 5) { + print "i is not big enough"; + break; + } + $i *= $factor; + if ($i < $minimum_limit) { + break; + } + print "i is ok"; + ...process i... + } while(0); + </programlisting> + </informalexample> + + <simpara> + Don't worry if you don't understand this right away or at all. + You can code scripts and even powerful scripts without using this + `feature'. + + <sect2 id="construct.for"> + <title><literal>for</literal></title> + + <para> + <literal>for</literal> loops are the most complex loops in + PHP. They behave like their C counterparts. The syntax of a + <literal>for</literal> loop is: + + <informalexample> + <programlisting> +for (expr1; expr2; expr3) statement + </programlisting> + </informalexample> + + <simpara> + The first expression (<replaceable>expr1</replaceable>) is evaluated + (executed) once unconditionally at the beginning of the loop. + + <simpara> + In the beginning of each iteration, <replaceable>expr2</replaceable> + is evaluated. If it evaluates to <literal>TRUE</literal>, the + loop continues and the nested statement(s) are executed. If it + evaluates to <literal>FALSE</literal>, the execution of the loop ends. + + <simpara> + At the end of each iteration, <replaceable>expr3</replaceable> + is evaluated (executed). + + <simpara> + Each of the expressions can be empty. + <replaceable>expr2</replaceable> being empty means + the loop should be run indefinitely (PHP implicitly + considers it as <literal>TRUE</literal>, like C). + This may not be as useless as you might think, since + often you'd want to end the loop using a conditional <link + linkend="construct.break"><literal>break</literal></link> statement + instead of using the <literal>for</literal> truth expression. + + <para> + Consider the following examples. All of them display numbers from + 1 to 10: + + <informalexample> + <programlisting> + /* example 1 */ + + for ($i = 1; $i <= 10; $i++) { + print $i; + } + + /* example 2 */ + + for ($i = 1;;$i++) { + if ($i > 10) { + break; + } + print $i; + } + + /* example 3 */ + + $i = 1; + for (;;) { + if ($i > 10) { + break; + } + print $i; + $i++; + } + + /* example 4 */ + + for ($i = 1; $i <= 10; print $i, $i++) ; + </programlisting> + </informalexample> + + <simpara> + Of course, the first example appears to be the nicest one (or + perhaps the fourth), but you may find that being able to use empty + expressions in <literal>for</literal> loops comes in handy in + many occasions. + + <para> + PHP also supports the alternate "colon syntax" for + <literal>for</literal> loops. + + <informalexample> + <programlisting> + for (expr1; expr2; expr3): statement; ...; endfor; + </programlisting> + </informalexample> + + <para> + Other languages have a foreach statement to traverse an array or + hash. PHP uses the while statement and the <function>list</function> + and <function>each</function> functions for this. See the + documentation for these functions for an example. + + + <sect2 id="construct.break"> + <title><literal>break</literal></title> + + <para> + <literal>break</literal> breaks out of the current looping construct. + + <informalexample> + <programlisting> + $i = 0; + while ($i < 10) { + if ($arr[$i] == "stop") { + break; + } + $i++; + } + </programlisting> + </informalexample> + + <sect2 id="construct.continue"> + <title><literal>continue</literal></title> + + <para> + <literal>continue</literal> jumps to the beginning of enclosing the looping + construct. + + <informalexample> + <programlisting> + while (list($key,$value) = each($arr)) { + if ($key % 2) { // skip even members + continue; + } + do_something_odd ($value); + } + </programlisting> + </informalexample> + + <sect2 id="construct.switch"> + <title><literal>switch</literal></title> + + <simpara> + The <literal>switch</literal> statement is similar to a series + of IF statements on the same expression. In many occasions, + you may want to compare the same variable (or expression) with + many different values, and execute a different piece of code + depending on which value it equals to. This is exactly what the + <literal>switch</literal> statement is for. + + <para> + The following two examples are two different ways to write the + same thing, one using a series of <literal>if</literal> statements, + and the other using the <literal>switch</literal> statement: + + <informalexample> + <programlisting> + /* example 1 */ + + if ($i == 0) { + print "i equals 0"; + } + if ($i == 1) { + print "i equals 1"; + } + if ($i == 2) { + print "i equals 2"; + } + + /* example 2 */ + + switch ($i) { + case 0: + print "i equals 0"; + break; + case 1: + print "i equals 1"; + break; + case 2: + print "i equals 2"; + break; + } + </programlisting> + </informalexample> + + <para> + It is important to understand how the <literal>switch</literal> + statement is executed in order to avoid messups. The + <literal>switch</literal> statement executes line by line (actually, + statement by statement). In the beginning, no code is executed. + Only when a <literal>case</literal> statement is found with a value that matches the + value of the <literal>switch</literal> expression, PHP begins to + execute the statements. PHP continues to execute the statements + until the end of the <literal>switch</literal> block, or the first + time it sees a <literal>break</literal> statement. If you don't + write a <literal>break</literal> statement at the end of a case's + statement list, PHP will go on executing the statements of the + following case. For example: + + <informalexample> + <programlisting> + /* example 3 */ + + switch ($i) { + case 0: + print "i equals 0"; + case 1: + print "i equals 1"; + case 2: + print "i equals 2"; + } + </programlisting> + </informalexample> + + <simpara> + Here, if $i equals to 0, PHP would execute all of the print + statements! If $i equals to 1, PHP would execute the last + two print statements, and only if $i equals to 2, you'd get the + 'expected' behavior and only 'i equals 2' would be displayed. So, + it's important not to forget <literal>break</literal> statements + (even though you may want to avoid supplying them on purpose under + certain circumstances). + + <para> + A special case is the default case. This case matches anything + that wasn't matched by the other cases. For example: + + <informalexample> + <programlisting> + /* example 4 */ + + switch ($i) { + case 0: + print "i equals 0"; + break; + case 1: + print "i equals 1"; + break; + case 2: + print "i equals 2"; + break; + default: + print "i is not equal to 0, 1 or 2"; + } + </programlisting> + </informalexample> + + <para> + Another fact worth mentioning is that the <literal>case</literal> + expression may be any expression that evaluates to a scalar type, + that is, integer or floating-point numbers and strings. Arrays or + objects are meaningless in that context. + + <sect2 id="function.require"> + <title><literal>require</literal></title> + + <simpara> + The <literal>require</literal> statement replaces itself with the + specified file, much like the C preprocessor's #include works. + + <para> + This means that you can't put a <literal>require</literal> + statement inside of a loop structure and expect it to include the + contents of a different file on each iteration. To do that, use an + <literal>include</literal> statement. + + <informalexample> + <programlisting> + require 'header.inc'; + </programlisting> + </informalexample> + + <sect2 id="function.include"> + <title><literal>include</literal></title> + + <simpara> + The <literal>include</literal> statement includes and evaluates + the specified file. + + <para> + This happens each time the <literal>include</literal> statement is + encountered, so you can use an <literal>include</literal> statement + within a looping structure to include a number of different file. + + <informalexample> + <programlisting> + $files = array ('first.inc', 'second.inc', 'third.inc'); + for ($i = 0; $i < count($files); $i++) { + include $files[$i]; + } + </programlisting> + </informalexample> + + <para> + <link linkend="function.include"><literal>include</literal></link> + differs from <link + linkend="function.require"><literal>require</literal></link> + in that the include statement is re-evaluated each time it is + encountered (and only when it is being executed), whereas the + <link linkend="function.require"><literal>require</literal></link> + statement is replaced by the required file when it is first + encountered, whether the contents of the file will be evaluated or + not (for example, if it is inside an if statement whose condition + evaluated to false). + + <para> + Because <link + linkend="function.include"><literal>include</literal></link> is a + special language construct, you must enclose it within a statement + block if it is inside a conditional block. + + <informalexample> + <programlisting> + /* This is WRONG and will not work as desired. */ + + if ($condition) + include($file); + else + include($other); + + /* This is CORRECT. */ + + if ($condition) { + include($file); + } else { + include($other); + } + </programlisting> + </informalexample> + + <para> + When the file is evaluated, the parser begins in "HTML-mode" which + will output the contents of the file until the first PHP start tag + (<?) is encountered. + + <para> + See also <function>readfile</function>, <function>require</function>, + <function>virtual</function>. + + <sect2 id="keyword.function"> + <title><literal>function</literal></title> + + <para> + A function may be defined using syntax such as the following: + + <informalexample> + <programlisting> + function foo ($arg_1, $arg_2, ..., $arg_n) { + echo "Example function.\n"; + return $retval; + } + </programlisting> + </informalexample> + + <simpara> + Any valid PHP code may appear inside a function, even other + functions and <link linkend="keyword.class">class</link> + definitions. + + <simpara> + Functions must be defined before they are referenced. + + <sect3 id="keyword.function.return"> + <title>Returning values</title> + + <para> + Values are returned by using the optional return statement. Any + type may be returned, including lists and objects. + + <informalexample> + <programlisting> + function my_sqrt ($num) { + return $num * $num; + } + echo my_sqrt (4); // outputs '16'. + </programlisting> + </informalexample> + + <para> + Multiple values may not be returned, but the same effect can be + achieved by returning a list: + + <informalexample> + <programlisting> + function foo() { + return array (0, 1, 2); + } + list ($zero, $one, $two) = foo(); + </programlisting> + </informalexample> + + </sect3> + + <sect3 id="keyword.function.arguments"> + <title>Arguments</title> + + <simpara> + Information may be passed to functions via the argument list, + which is a comma-delimited list of variables and/or constants. + + <para> + PHP supports passing arguments by value (the default), <link + linkend="keyword.function.arguments.reference">passing by + reference</link>, and <link + linkend="keyword.function.arguments.default">default argument + values</link>. Variable-length argument lists are not supported, + but a similar effect may be achieved by passing arrays. + + <informalexample> + <programlisting> + function takes_array($input) { + echo "$input[0] + $input[1] = ", $input[0]+$input[1]; + } + </programlisting> + </informalexample> + + <sect4 id="keyword.function.arguments.reference"> + <title>Passing by reference</title> + + <simpara> + By default, function arguments are passed by value. If you wish + to allow a function to modify its arguments, you may pass them + by reference. + + <para> + If you wish a function's argument to always be passed by + reference, you can prepend an ampersand (&) to the argument + name in the function definition: + + <informalexample> + <programlisting> + function foo( &$bar ) { + $bar .= 'and something extra.'; + } + $str = 'This is a string, '; + foo ($str); + echo $str; // outputs 'This is a string, and something extra.' + </programlisting> + </informalexample> + + <para> + If you wish to pass a variable by reference to a function which + does not do this by default, you may prepend an ampersand to the + argument name in the function call: + + <informalexample> + <programlisting> + function foo ($bar) { + $bar .= ' and something extra.'; + } + $str = 'This is a string, '; + foo ($str); + echo $str; // outputs 'This is a string, ' + foo (&$str); + echo $str; // outputs 'This is a string, and something extra.' + </programlisting> + </informalexample> + + </sect4> + + <sect4 id="keyword.function.arguments.default"> + <title>Default values</title> + + <para> + A function may define C++-style default values for scalar + arguments as follows: + + <informalexample> + <programlisting> + function makecoffee ($type = "cappucino") { + echo "Making a cup of $type.\n"; + } + echo makecoffee (); + echo makecoffee ("espresso"); + </programlisting> + </informalexample> + + <para> + The output from the above snippet is: + + <screen> + Making a cup of cappucino. + Making a cup of espresso. + </screen> + + <simpara> + The default value must be a constant expression, not (for + example) a variable or class member. + + <para> + Note that when using default arguments, any defaults should be + on the right side of any non-default arguments; otherwise, + things will not work as expected. Consider the following code + snippet: + + <informalexample> + <programlisting> + function makeyogurt ($type = "acidophilus", $flavour) { + return "Making a bowl of $type $flavour.\n"; + } + + echo makeyogurt ("raspberry"); // won't work as expected + </programlisting> + </informalexample> + + <para> + The output of the above example is: + + <screen> + Warning: Missing argument 2 in call to makeyogurt() in + /usr/local/etc/httpd/htdocs/php3test/functest.html on line 41 + Making a bowl of raspberry . + </screen> + + <para> + Now, compare the above with this: + + <informalexample> + <programlisting> + function makeyogurt ($flavour, $type = "acidophilus") { + return "Making a bowl of $type $flavour.\n"; + } + + echo makeyogurt ("raspberry"); // works as expected + </programlisting> + </informalexample> + + <para> + The output of this example is: + + <screen> + Making a bowl of acidophilus raspberry. + </screen> + + </sect4> + + </sect3> + + </sect2> + + + <sect2 id="keyword.old-function"> + <title><literal>old_function</literal></title> + + <simpara> + The <literal>old_function</literal> statement allows you to declare + a function using a syntax identical to PHP/FI2 (except you must + replace 'function' with 'old_function'. + <simpara> + This is a deprecated feature, and should only be used by the + PHP/FI2->PHP3 convertor. + <simpara> + Functions declared as <literal>old_function</literal> + cannot be called from PHP's internal code. Among other + things, this means you can't use them in functions such as + <function>usort</function>, <function>array_walk</function>, and + <function>register_shutdown_function</function>. You can get around + this limitation by writing a wrapper function (in normal PHP3 form) + to call the <literal>old_function</literal>. + </sect2> + + <sect2 id="keyword.class"> + <title><literal>class</literal></title> + <para> + A class is a collection of variables and functions working with + these variables. A class is defined using the following syntax: + + <informalexample> + <programlisting role=php> + <?php + class Cart { + var $items; // Items in our shopping cart + + // Add $num articles of $artnr to the cart + + function add_item ($artnr, $num) { + $this->items[$artnr] += $num; + } + + // Take $num articles of $artnr out of the cart + + function remove_item ($artnr, $num) { + if ($this->items[$artnr] > $num) { + $this->items[$artnr] -= $num; + return true; + } else { + return false; + } + } + } + ?> + </programlisting> + </informalexample> + + <para> + This defines a class named Cart that consists of an associative + array of articles in the cart and two functions to add and remove + items from this cart. + + </para><para> + Classes are types, that is, they are blueprints for actual + variables. You have to create a variables of the desired type with + the new operator. + </para> + + <informalexample> + <programlisting role=php> + $cart = new Cart; + $cart->add_item("10", 1); + </programlisting> + </informalexample> + + <para> + This creates an object $cart of the class Cart. The function + add_item() of that object is being called to add 1 item of article + number 10 to the cart. + </para><para> + Classes can be extensions of other classes. The extended or + derived class has all variables and functions of the base class + and what you add in the extended definition. This is done using + the extends keyword. + </para> + + <informalexample> + <programlisting role=php> + class Named_Cart extends Cart { + var $owner; + + function set_owner ($name) { + $this->owner = $name; + } + } + </programlisting> + </informalexample> + + <para> + This defines a class Named_Cart that has all variables and + functions of Cart plus an additional variable $owner and an + additional function set_owner(). You create a named cart the usual + way and can now set and get the carts owner. You can still use + normal cart functions on named carts: + </para> + + <informalexample> + <programlisting role=php> + $ncart = new Named_Cart; // Create a named cart + $ncart->set_owner ("kris"); // Name that cart + print $ncart->owner; // print the cart owners name + $ncart->add_item ("10", 1); // (inherited functionality from cart) + </programlisting> + </informalexample> + + <para> + Within functions of a class the variable $this means this + object. You have to use $this->something to access any variable or + function named something within your current object. + </para> + + <para> + Constructors are functions in a class that are automatically + called when you create a new instance of a class. A function + becomes a constructor when it has the same name as the class. + </para> + + <informalexample> + <programlisting role=php> + class Auto_Cart extends Cart { + function Auto_Cart () { + $this->add_item ("10", 1); + } + } + </programlisting> + </informalexample> + + <para> + This defines a class Auto_Cart that is a Cart plus a constructor + which initializes the cart with one item of article number "10" + each time a new Auto_Cart is being made with "new". Constructors + can also take arguments and these arguments can be optional, which + makes them much more useful. + </para> + + <informalexample> + <programlisting role=php> + class Constructor_Cart { + function Constructor_Cart ($item = "10", $num = 1) { + $this->add_item ($item, $num); + } + } + + // Shop the same old boring stuff. + + $default_cart = new Constructor_Cart; + + // Shop for real... + + $different_cart = new Constructor_Cart ("20", 17); + </programlisting> + </informalexample> + + <caution> + <simpara> + For derived classes, the constructor of the parent class is not + automatically called when the derived class's constructor is called. + </caution> + + </chapter> + +  -- PHP Development Mailing List http://www.php.net/ To unsubscribe send an empty message to php-dev-unsubscribe@lists.php.net For help: php-dev-help@lists.php.net