Is there a way to get the name of a variable? PHP - Reflection

Question

I know this is not exactly reflection, but kind of. I want to make a debug function that gets a variable and prints a var_dump and the variable name.

Of course, when the programmer writes a call to the function, they already know the variable's name, so they could write something like:

debug( $myvar, 'myvar' );

But I want it to be quick and easy to write, just the function name, the variable, and voilà !

debug( $myvar ); // quicker and easier :)

Answer 1

You can do it by converting the variable to a key/value set before passing it to the function.

function varName($theVar) {  
   $variableName = key($theVar);  
   $variableValue = $theVar[$variableName];  
   echo ('The name of the variable used in the function call was '.$variableName.'<br />');  
   echo ('The value of the variable used in the function call was '.$variableValue.'<br />');  
}
$myVar = 'abc';
varName(compact('myVar'));

Though I don't recommend creating a reference to a nameless variable, function varName(&$theVar) works too.

Since compact() takes the variable name as a string rather than the actual variable, iterating over a list of variable names should be easy.

As to why you would want to do this -- don't ask me but it seems like a lot of people ask the question so here's my solution.

Answer 2

I know I'm answering a 4 year old question but what the hell...

compact() might help you is your friend here!

I made a similar function to quickly dump out info on a few chosen variables into a log for debugging errors and it goes something like this:

function vlog() {
    $args = func_get_args();
    foreach ($args as $arg) {
        global ${$arg};
    }
    return json_encode(compact($args));
}

I found JSON to be the cleanest and most readable form for these dumps for my logs but you could also use something like print_r() or var_export().

This is how I use it:

$foo = 'Elvis';
$bar = 42;
$obj = new SomeFancyObject();

log('Something went wrong! vars='.vlog('foo', 'bar', 'obj'));

And this would print out like this to the logs:

Something went wrong! vars={"foo":"Elvis","bar":42,"obj":{"nestedProperty1":1, "nestedProperty2":"etc."}}

Word of warning though: This will only work for variables declared in the global scope (so not inside functions or classes. In there you need to evoke compact() directly so it has access to that scope, but that's not really that big of a deal since this vlog() is basically just a shortcut for json_encode(compact('foo', 'bar', 'obj')), saving me 16 keystrokes each time I need it.

Answer 3

Nope, not possible. Sorry.

Answer 4

Not elegantly... BUT YOU COULD FAKE IT!

• 1) Drink enough to convince yourself this is a good idea (it'll take a lot)
• 2) Replace all your variables with variable variables:

$a = 10
//becomes
$a = '0a';
$$a = 10;

• 3) Reference $$a in all your code.
• 4) When you need to print the variable, print $a and strip out the leading 0.

Addendum: Only do this if you are

• Never showing this code to anyone
• Never need to change or maintain this code
• Are crazy
• Not doing this for a job
• Look, just never do this, it is a joke

Answer 5

I know this is very very late, but i did it in a different way.

It might honestly be a bit bad for performance, but since it's for debugging it shouldn't be a problem.

I read the file where the function is called, on the line it was called and I cut out the variable name.

function dump($str){
    // Get the caller with debug backtrace
    $bt = debug_backtrace();
    $caller = array_shift($bt);

    // Put the file where the function was called in an array, split by lines
    $readFileStr = file($caller['file']);

    // Read the specific line where the function was called
    $lineStr = $readFileStr[$caller['line'] -1];

    // Get the variable name (including $) by taking the string between '(' and ')'
    $regularOutput = preg_match('/\((.*?)\)/', $lineStr, $output);
    $variableName = $output[1];

    // echo the var name and in which file and line it was called
    echo "var: " . $variableName . " dumped in file: " . $caller['file'] . ' on line: ' . $caller['line'] . '<br>';

    // dump the given variable
    echo '<pre>' . var_export($str, true) . '</pre>';
}

Answer 6

No, the closer you will get is with get_defined_vars().

EDIT: I was wrong, after reading the user comments on get_defined_vars() it's possible with a little hack:

function ev($variable){
    foreach($GLOBALS as $key => $value){
        if($variable===$value){
            echo '<p>$'.$key.' - '.$value.'</p>';
        }
    }
}

$lol = 123;

ev($lol); // $lol - 123

Only works for unique variable contents though.

Answer 7

i've had the same thought before, but if you really think about it, you'll see why this is impossible... presumably your debug function will defined like this: function debug($someVar) { } and there's no way for it to know the original variable was called $myvar.

The absolute best you could do would be to look at something like get_defined_vars() or $_GLOBALS (if it were a global for some reason) and loop through that to find something which matches the value of your variable. This is a very hacky and not very reliable method though. Your original method is the most efficient way.

Answer 8

Bit late to the game here, but Mach 13 has an interesting solution: How to get a variable name as a string in PHP

Answer 9

You could use eval:

function debug($variablename)
{
  echo ($variablename . ":<br/>");
  eval("global $". $variablename . ";");
  eval("var_dump($" . $variablename . ");");
}

Usage: debug("myvar") not debug($myvar)

Answer 10

This is late post but I think it is possible now using compact method

so the code would be

$a=1;
$b=2;
$c=3

var_dump(compact('a','b','c'));

the output would be

array (size=3)
'a' => int 1
'b' => int 2
'c' => int 3

where variable name a, b and c are the key

Hope this helps

Answer 11

I believe Alix and nickf are suggesting this:

function debug($variablename)
{
  echo ($variablename . ":<br/>");
  global $$variablename; // enable scope
  var_dump($$variablename);
}

I have tested it and it seems to work just as well as Wagger's code (Thanks Wagger: I have tried so many times to write this and the global variable declaration was my stumbling block)