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

user_13227 0
Viewed 206804

Say i have this PHP code:

$FooBar = "a string";

i then need a function like this:

print_var_name($FooBar);

which prints:

FooBar

Any Ideas how to achieve this? Is this even possible in PHP?

php
26 Answers

I couldn't think of a way to do this efficiently either but I came up with this. It works, for the limited uses below.

shrug

<?php

function varName( $v ) {
    $trace = debug_backtrace();
    $vLine = file( __FILE__ );
    $fLine = $vLine[ $trace[0]['line'] - 1 ];
    preg_match( "#\\$(\w+)#", $fLine, $match );
    print_r( $match );
}

$foo = "knight";
$bar = array( 1, 2, 3 );
$baz = 12345;

varName( $foo );
varName( $bar );
varName( $baz );

?>

// Returns
Array
(
    [0] => $foo
    [1] => foo
)
Array
(
    [0] => $bar
    [1] => bar
)
Array
(
    [0] => $baz
    [1] => baz
)

It works based on the line that called the function, where it finds the argument you passed in. I suppose it could be expanded to work with multiple arguments but, like others have said, if you could explain the situation better, another solution would probably work better.

user_409060

You could use get_defined_vars() to find the name of a variable that has the same value as the one you're trying to find the name of. Obviously this will not always work, since different variables often have the same values, but it's the only way I can think of to do this.

Edit: get_defined_vars() doesn't seem to be working correctly, it returns 'var' because $var is used in the function itself. $GLOBALS seems to work so I've changed it to that.

function print_var_name($var) {
    foreach($GLOBALS as $var_name => $value) {
        if ($value === $var) {
            return $var_name;
        }
    }

    return false;
}

Edit: to be clear, there is no good way to do this in PHP, which is probably because you shouldn't have to do it. There are probably better ways of doing what you're trying to do.

Jeremy_Ruten_8130

You might consider changing your approach and using a variable variable name?

$var_name = "FooBar";
$$var_name = "a string";

then you could just 

print($var_name);

to get 

FooBar

Here's the link to the PHP manual on Variable variables

Admin1

I made an inspection function for debugging reasons. It's like print_r() on steroids, much like Krumo but a little more effective on objects. I wanted to add the var name detection and came out with this, inspired by Nick Presta's post on this page. It detects any expression passed as an argument, not only variable names.

This is only the wrapper function that detects the passed expression. Works on most of the cases. It will not work if you call the function more than once in the same line of code.

This works fine: die(inspect($this->getUser()->hasCredential("delete")));

inspect() is the function that will detect the passed expression.

We get: $this->getUser()->hasCredential("delete")

function inspect($label, $value = "__undefin_e_d__")
{
    if($value == "__undefin_e_d__") {

        /* The first argument is not the label but the 
           variable to inspect itself, so we need a label.
           Let's try to find out it's name by peeking at 
           the source code. 
        */

        /* The reason for using an exotic string like 
           "__undefin_e_d__" instead of NULL here is that 
           inspected variables can also be NULL and I want 
           to inspect them anyway.
        */

        $value = $label;

        $bt = debug_backtrace();
        $src = file($bt[0]["file"]);
        $line = $src[ $bt[0]['line'] - 1 ];

        // let's match the function call and the last closing bracket
        preg_match( "#inspect\((.+)\)#", $line, $match );

        /* let's count brackets to see how many of them actually belongs 
           to the var name
           Eg:   die(inspect($this->getUser()->hasCredential("delete")));
                  We want:   $this->getUser()->hasCredential("delete")
        */
        $max = strlen($match[1]);
        $varname = "";
        $c = 0;
        for($i = 0; $i < $max; $i++){
            if(     $match[1]{$i} == "(" ) $c++;
            elseif( $match[1]{$i} == ")" ) $c--;
            if($c < 0) break;
            $varname .=  $match[1]{$i};
        }
        $label = $varname;
    }

    // $label now holds the name of the passed variable ($ included)
    // Eg:   inspect($hello) 
    //             => $label = "$hello"
    // or the whole expression evaluated
    // Eg:   inspect($this->getUser()->hasCredential("delete"))
    //             => $label = "$this->getUser()->hasCredential(\"delete\")"

    // now the actual function call to the inspector method, 
    // passing the var name as the label:

      // return dInspect::dump($label, $val);
         // UPDATE: I commented this line because people got confused about 
         // the dInspect class, wich has nothing to do with the issue here.

    echo("The label is: ".$label);
    echo("The value is: ".$value);

}

Here's an example of the inspector function (and my dInspect class) in action:

http://inspect.ip1.cc

Texts are in spanish in that page, but code is concise and really easy to understand.

user_2902210

Many replies question the usefulness of this. However, getting a reference for a variable can be very useful. Especially in cases with objects and $this. My solution works with objects, and as property defined objects as well:

function getReference(&$var)
{
    if(is_object($var))
        $var->___uniqid = uniqid();
    else
        $var = serialize($var);
    $name = getReference_traverse($var,$GLOBALS);
    if(is_object($var))
        unset($var->___uniqid);
    else
        $var = unserialize($var);
    return "\${$name}";    
}

function getReference_traverse(&$var,$arr)
{
    if($name = array_search($var,$arr,true))
        return "{$name}";
    foreach($arr as $key=>$value)
        if(is_object($value))
            if($name = getReference_traverse($var,get_object_vars($value)))
                return "{$key}->{$name}";
}

Example for the above:

class A
{
    public function whatIs()
    {
        echo getReference($this);
    }
}

$B = 12;
$C = 12;
$D = new A;

echo getReference($B)."<br/>"; //$B
echo getReference($C)."<br/>"; //$C
$D->whatIs(); //$D
user_12729780

If the variable is interchangable, you must have logic somewhere that's determining which variable gets used. All you need to do is put the variable name in $variable within that logic while you're doing everything else.

I think we're all having a hard time understanding what you're needing this for. Sample code or an explanation of what you're actually trying to do might help, but I suspect you're way, way overthinking this.

ceejayoz_19020100

I actually have a valid use case for this.

I have a function cacheVariable($var) (ok, I have a function cache($key, $value), but I'd like to have a function as mentioned).

The purpose is to do:

$colour = 'blue';
cacheVariable($colour);

...

// another session

...

$myColour = getCachedVariable('colour');

I have tried with 

function cacheVariable($variable) {
   $key = ${$variable}; // This doesn't help! It only gives 'variable'.
   // do some caching using suitable backend such as apc, memcache or ramdisk
}

I have also tried with

function varName(&$var) {
   $definedVariables = get_defined_vars();
   $copyOfDefinedVariables = array();
   foreach ($definedVariables as $variable=>$value) {
      $copyOfDefinedVariables[$variable] = $value;
   }
   $oldVar = $var;
   $var = !$var;
   $difference = array_diff_assoc($definedVariables, $copyOfDefinedVariables);
   $var = $oldVar;
   return key(array_slice($difference, 0, 1, true));
}

But this fails as well... :(

Sure, I could continue to do cache('colour', $colour), but I'm lazy, you know... ;)

So, what I want is a function that gets the ORIGINAL name of a variable, as it was passed to a function. Inside the function there is no way I'm able to know that, as it seems. Passing get_defined_vars() by reference in the second example above helped me (Thanks to Jean-Jacques Guegan for that idea) somewhat. The latter function started working, but it still only kept returning the local variable ('variable', not 'colour').

I haven't tried yet to use get_func_args() and get_func_arg(), ${}-constructs and key() combined, but I presume it will fail as well.

user_1509260

Here's my solution based on Jeremy Ruten

class DebugHelper {

    function printVarNames($systemDefinedVars, $varNames) {
        foreach ($systemDefinedVars as $var=>$value) {
            if (in_array($var, $varNames )) {
                var_dump($var);
                var_dump($value);
            }
        }
    }
}

using it

DebugHelper::printVarNames(
    $systemDefinedVars = get_defined_vars(),
    $varNames=array('yourVar00', 'yourVar01')
);
user_9318770

This is the way I did it

function getVar(&$var) {
    $tmp = $var; // store the variable value
    $var = '_$_%&33xc$%^*7_r4'; // give the variable a new unique value
    $name = array_search($var, $GLOBALS); // search $GLOBALS for that unique value and return the key(variable)
    $var = $tmp; // restore the variable old value
    return $name;
}

Usage

$city  = "San Francisco";
echo getVar($city); // city

Note: some PHP 7 versions will not work properly due to a bug in array_search with $GLOBALS, however all other versions will work.

See this https://3v4l.org/UMW7V

user_59993720

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. Here is an example:

<?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);
?>

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

user_129033960

I know this is old and already answered but I was actually looking for this. I am posting this answer to save people a little time refining some of the answers.

Option 1: 

$data = array('$FooBar');  

$vars = [];  
$vars = preg_replace('/^\\$/', '', $data); 

$varname = key(compact($vars));  
echo $varname;

Prints:

FooBar

For whatever reason you would find yourself in a situation like this, it does actually work.

.
Option 2: 

$FooBar = "a string";  

$varname = trim(array_search($FooBar, $GLOBALS), " \t.");  
echo $varname;

If $FooBar holds a unique value, it will print 'FooBar'. If $FooBar is empty or null it will print the name of the first empty or null string it finds.

It could be used as such: 

if (isset($FooBar) && !is_null($FooBar) && !empty($FooBar)) {
    $FooBar = "a string";
    $varname = trim(array_search($FooBar, $GLOBALS), " \t.");
}
user_54117360

other use:

shrug

function varsToArrayAssoc(...$arguments){
  
    $bt   = debug_backtrace();
    $file = file($bt[0]['file']);
    $src  = $file[$bt[0]['line']-1];
    $pat = '#(.*)'.__FUNCTION__.' *?\( *?(.*) *?\)(.*)#i';
    $vars  =explode(',',substr_replace(trim(preg_replace($pat, '$2', $src)) ,"", -1));
    $result=[];
    foreach(func_get_args() as $key=>$v){
        $index=trim(explode('$',$vars[$key])[1]);
        $result[$index]=$v;
    }
    return $result;
}

$a=12;
$b=13;
$c=123;
$d='aa';

var_dump(varsToArrayAssoc($a,$b,$c,$d));
user_30836310

I really fail to see the use case... If you will type print_var_name($foobar) what's so hard (and different) about typing print("foobar") instead?

Because even if you were to use this in a function, you'd get the local name of the variable...

In any case, here's the reflection manual in case there's something you need in there.

Vinko_Vrsalovic_51900
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