From: http://mach13.com/how-to-get-a-variable-name-as-a-string-in-php
How to get a variable name as a string in PHP
PHP – Jean-Jacques Guegan
On rare occasions, you may need to retrieve a variable name as a string.
This handy little function retreives the name of the variable:
< ?php
$my_var = 1;
echo var_name ($my_var);
?>
will give ‘my_var’.
I started trying to find a solution to this problem, because I needed such a function and because questions about it appeared on several mailing lists and forums:
[PHP] Is there a way to get a variable name as a string?
most people said it was not possible…
Re: [PHP] Is there a way to get a variable name as a string?
From: Rasmus Lerdorf
In PHP it is possible to use a variable if you have its name as a string :
< ?php
$iVarName = 'MaxSize';
$$iVarName = 10;
echo $MaxSize;
?>
But PHP does not natively include a way to get the name of a given variable.
This might be useful in situations where you design a function with a parameter passed by reference and you need to know which variable was sent as a parameter for this function.
The solution :
The following function retreives the variable name from a given variable:
< ?php
function var_name (&$iVar, &$aDefinedVars)
{
foreach ($aDefinedVars as $k=>$v)
$aDefinedVars_0[$k] = $v;
$iVarSave = $iVar;
$iVar =!$iVar;
$aDiffKeys = array_keys (array_diff_assoc ($aDefinedVars_0, $aDefinedVars));
$iVar = $iVarSave;
return $aDiffKeys[0];
}
?>
This function has to be called with a second parameter always set to the result of the function “get_defined_vars()”:
< ?php var_name($iVar, get_defined_vars()); ?>
How does it work ?
var_name compares the result of the function “get_defined_vars()” before and after modification of the variable whose name we want to find.
The initial set of defined variables passed as a parameter to var_name is first stored in “$aDefinedVars_0” and compared later.
Before modifying the value of the variable, its value is saved in $iVarSave.
$iVar
is then changed to something different :
$iVar=!$iVar;
$aDefinedVars keeps track of this modification and can be compare to $aDefinedVars_0 (its initial value). The difference is the variable we modified and we can get its name as a string in the key value of the array record.
The value of the variable is restored to its initial value kept in $iVarSave and the name of the variable is returned.
Example :
The following PHP code shows the function var_name in action:
< ?php $v_1 = 1; echo 'var $',var_name ($v_1, get_defined_vars()),' = ',var_dump($v_1),'
'; $v_2 = 4; echo 'var $',var_name ($v_2, get_defined_vars()),' = ',var_dump($v_2),'
'; $v_3 = 'qwerty'; echo 'var $',var_name ($v_3, get_defined_vars()),' = ',var_dump($v_3),'
'; $v_4 = array('aa'=>'11','bb'=>'22',3); echo 'var $',var_name ($v_4, get_defined_vars()),' = ',var_dump($v_4),'
'; $v_5 = &$v_2; echo 'var $',var_name ($v_5, get_defined_vars()),' = ',var_dump($v_5),'
'; echo 'var $',implode (' / $',var_name ($v_5, get_defined_vars(),true)),' = ',var_dump($v_5),'
'; function test() { $v_1 = 'qwerty'; echo 'var $',var_name ($v_1, get_defined_vars()),' = ',var_dump($v_1),'
'; global $v_5; echo 'var $',var_name ($v_5, get_defined_vars()),' = ',var_dump($v_5),'
'; } test(); ?>
var_name can retreive the name of the variable in every case.
Application :
The most direct application of this function is, of course, a “dump” function.
Just call this “dump” function with the variable you want to monitor – do not forget to add the “get_defined_vars()” parameter…
< ?php
function dump(&$v, &$aDefinedVars)
{
echo '
',implode (' / $',var_name ($v, $aDefinedVars, true)),' = ',print_r($v, true),'
';
}
dump($v_4, get_defined_vars());
?>
Going further :
The function var_name can be enhanced by adding the parameter $bShowAllRef to show, if set to true, all the references relating to the variable passed as a parameter:
< ?php
function var_name (&$iVar, &$aDefinedVars, $bShowAllRef=false )
{
foreach ($aDefinedVars as $k=>$v)
$aDefinedVars_0[$k] = $v;
$iVarSave = $iVar;
$iVar =!$iVar;
$aDiffKeys = array_keys (array_diff_assoc ($aDefinedVars_0, $aDefinedVars));
$iVar = $iVarSave;
return ($bShowAllRef? $aDiffKeys: $aDiffKeys[0]);
}
?>
That’s it ! You can download the function here.
This code is free to use and published under the GPL license.
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