note 96407 modified in function.eval by danbrown
| From: | danbrown@php.net | Date: | Thu, 25 Feb 2010 18:39:12 +0000 |
| Subject: | note 96407 modified in function.eval by danbrown | ||
| References: | 1 | Groups: | php.notes |
| Request: | Send a blank email to php-notes+get-166357@lists.php.net to get a copy of this message | ||
A simple use of eval:
Sometimes you want to know both the value of a variable being passed to a function and its name.
Passing by reference can get you there, but only through a lot of convolutions (as far as I can
tell!)
But by using the stem of a variable's name, there are two methods to achieve this.
Say that
<?php
$emailName="me@example.com";
?>
You can pass this information thusly:
First, if you have the stem, "emailName', in a string var
<?php
$theVarStem="emailName";
?>
you can recover the value of the original variable like this:
<?php
$theVarValue=eval("return \$$theVarStem;");
?>
Using 'return' inside the eval is the trick that makes it work - something inherent in the
documentation but not at all obvious to me.
Unless $emailName has global scope, this method won't work inside a function. For that purpose,
you can do the following:
<?php
myFunction(compact("emailName"))
function myFunction($theInfo)
{
$theVarStem=key($theInfo);
$theVarValue=current($theInfo);
//...
}
?>
I apologize if all this seems too obvious: it took me a lotta sloggin' to figure it out.
--was--
A simple use of eval:
Sometimes you want to know both the value of a variable being passed to a function and its name.
Passing by reference can get you there, but only through a lot of convolutions (as far as I can
tell!)
But by using the stem of a variable's name, there are two methods to achieve this.
Say that
<?
$emailName="me@q.com";
?>
You can pass this information thusly:
First, if you have the stem, "emailName', in a string var
<?
$theVarStem="emailName";
?>
you can recover the value of the original variable like this:
<?
$theVarValue=eval("return \$$theVarStem;");
?>
Using 'return' inside the eval is the trick that makes it work - something inherent in the
documentation but not at all obvious to me.
Unless $emailName has global scope, this method won't work inside a function. For that purpose,
you can do the following:
<?
myFunction(compact("emailName"))
function myFunction($theInfo)
{
$theVarStem=key($theInfo);
$theVarValue=current($theInfo);
...
}
?>
I apologize if all this seems too obvious: it took me a lotta sloggin' to figure it out.
http://php.net/manual/en/function.eval.php