How to get a variable name as a string in PHP?

November 20, 2020 admin

In this tutorial, we’re going to see how to get the name of a variable by accessing get_defined_vars().

There is no predefined function in PHP that can output the name of a variable. However, you can use the result of get_defined_vars(), which returns all the variables defined in the scope, including name and value.

Definition of your own function

<?php
    // Function for determining the name of a variable
    function getVarName(&$var, $definedVars=null) {
        $definedVars = (!is_array($definedVars) ? $GLOBALS : $definedVars);
        $val = $var;
        $rand = 1;
        while (in_array($rand, $definedVars, true)) {
            $rand = md5(mt_rand(10000, 1000000));
        }
        $var = $rand;
         
        foreach ($definedVars as $dvName=>$dvVal) {
            if ($dvVal === $rand) {
                $var = $val;
                return $dvName;
            }
        }
         
        return null;
    }
 
    // the name of $a is to be determined.   
    $a = 1;
     
    // Determine the name of $a
    echo getVarName($a);
?>

Output:

The function getVarName() proceeds as follows:

The variable for which the name is to be determined is received as a reference. This is important because the value must be adjusted below.
The old value of the variable is saved.
The value of the variable is temporarily changed to a random value that does not yet appear among the defined variables.
The variable that has this random value is searched for among the defined variables.
The value of this variable is reset to the saved value.
The name of this variable is returned.

getVarName() in the scope of a function

In the previous example, the function was called in the global scope (top level). In this case, the result of get_defined_vars() does not have to be transferred, the function then automatically uses $GLOBALS. However, if you are in a function, then get_defined_vars() must be used once.

<?php
    // insert the getVarName function from the previous example here
 
 
    function myfunction() 
    {
        $a = 1;
        var_dump(getVarName($a)); // this call does not find $a
        var_dump(getVarName($a, get_defined_vars())); // with this it will be found
    }
 
    myfunction();
?>

Output: