Doc #54549 [Opn->Csd]: Using $variable--; and $variable -= '1'; yield different results.

Edit report at http://bugs.php.net/bug.php?id=54549&edit=1 ID: 54549 Updated by: salathe@php.net Reported by: account22a23 at hotmail dot com Summary: Using $variable--; and $variable -= '1'; yield different results. -Status: Open +Status: Closed Type: Documentation Problem Package: *Programming Data Structures Operating System: Fedora 14 PHP Version: 5.3.6 -Assigned To: +Assigned To: salathe Block user comment: N Private report: N New Comment: This bug has been fixed in SVN. Snapshots of the sources are packaged every three hours; this change will be in the next snapshot. You can grab the snapshot at http://snaps.php.net/. Thank you for the report, and for helping us make PHP better. Previous Comments: ------------------------------------------------------------------------ [2011-04-26 21:29:42] salathe@php.net Automatic comment from SVN on behalf of salathe Revision: http://svn.php.net/viewvc/?view=revision&amp;revision=310528 Log: decrementing, or incrementing non-A-Za-z, string variables has no effect (doc #54549) ------------------------------------------------------------------------ [2011-04-17 15:05:59] cataphract@php.net The post decrement operator has no effect on non-numeric strings. Your $int variable is not == "2"; its value is actually "2\n" (with a line break on the end), so you get no effect, as in: <?php $a = $b = "2\n"; $a--; var_dump($a === $b); //bool(true) Using $a -= '1'; works because this operation is more permissive on the first operand and takes "2\n" as if it were 2: decrement_function calls is_numeric_string with allow_errors=0 and sub_function with allow_errors=1. This should be documented. Also, you might want to use: echo 'dump of int: ', var_dump($int) instead of echo 'dump of int: ' . var_dump($int) because var_dump has side effects and by using ".", you're forcing it to be evaluated before anything is echoed. ------------------------------------------------------------------------ [2011-04-17 14:20:55] account22a23 at hotmail dot com Code was run from command line. ------------------------------------------------------------------------ [2011-04-17 14:19:54] hotmail22a23 at hotmail dot com Code was run from command line. ------------------------------------------------------------------------ [2011-04-17 14:03:37] account22a23 at hotmail dot com Description: ------------ While the code below may have other problems, the simple fact of the matter is that when I uncomment "$int--;" and comment "$int -= '1';" the code will loop for at least a minute, but when it is left as is below it does not and will terminate as expected. Since I've been told the two pieces of code have the exact same logic, I have no explaination for this. Please contact me if you know why. The php package was installed using 'yum install php php-mysql' on fedora 14. Test script: --------------- <?php function GeneratePassword($int, $string){ $new_string = ''; while ($int >= 0){ $new_string += $string[rand(0, (strlen($string) - 1))]; //$int--; $int -= '1'; echo 'round'; echo 'dump of int: ' . var_dump($int); echo 'dump of string: ' . var_dump($string); echo 'dump of new_string: ' . var_dump($new_string); } return ($new_string); } fwrite(STDOUT, "Choose an int"); $int = fgets(STDIN); fwrite(STDOUT, "Choose a string"); $string = fgets(STDIN); $pass = GeneratePassword($int, $string); echo 'anything'; echo $pass; ?> Actual result: -------------- CASE 1 USING: //$int--; $int -= '1'; ------------------------------------------------------ php -f delete_me2.php Choose an int2 Choose a stringbb roundint(1) dump of int: string(3) "bb " dump of string: int(0) dump of new_string: roundint(0) dump of int: string(3) "bb " dump of string: int(0) dump of new_string: roundint(-1) dump of int: string(3) "bb " dump of string: int(0) dump of new_string: anything0 CASE 2 USING: $int--; //$int -= '1'; ------------------------------------------------------ php -f delete_me2.php Choose an int2 Choose a stringbb roundstring(2) "2 " dump of int: string(3) "bb " dump of string: string(0) "" dump of new_string: roundstring(2) "2 " dump of int: string(3) "bb " dump of string: string(0) "" dump of new_string: roundstring(2) "2 " dump of int: string(3) "bb " dump of string: string(0) "" dump of new_string: roundstring(2) "2 " dump of int: string(3) "bb " dump of string: string(0) "" dump of new_string: roundstring(2) "2 " dump of int: string(3) "bb " dump of string: string(0) "" dump of new_string: roundstring(2) "2 " dump of int: string(3) "bb " dump of string: string(0) "" dump of new_string: roundstring(2) "2 " dump of int: string(3) "bb " dump of string: string(0) "" dump of new_string: roundstring(2) "2 " dump of int: string(3) "bb " dump of string: string(0) "" dump of new_string: roundstring(2) "2 " dump of int: string(3) "bb " dump of string: string(0) "" dump of new_string: roundstring(2) "2 " dump of int: string(3) "bb " dump of string: string(0) "" dump of new_string: roundstring(2) "2 " dump of int: string(3) "bb " dump of string: string(0) "" dump of new_string: roundstring(2) "2 " ... (loops for at least 60 seconds) ... ------------------------------------------------------------------------ -- Edit this bug report at http://bugs.php.net/bug.php?id=54549&edit=1