I have a strange question that's probably not possible, but it's worth asking in case there are any PHP internals nerds who know a way to do it. Is there any way to get the variable name from a function call within PHP? It'd be easier to give an example:
function fn($argument) {
echo SOME_MAGIC_FUNCTION();
}
$var1 = "foo";
$var2 = "bar";
fn($var1); // outputs "$var1", not "foo"
fn($var2); // outputs "$var2", not "bar"
Before you say it - yes, I know this would be a terrible idea with no use in production code. However, I'm migrating some old code to new code, and this would allow me to very easily auto-generate the replacement code. Thanks!
debug_backtrace() returns information about the current call stack, including the file and line number of the call to the current function. You could read the current script and parse the line containing the call to find out the variable names of the arguments.
A test script with debug_backtrace:
<?php
function getFirstArgName() {
$calls=debug_backtrace();
$nearest_call=$calls[1];
$lines=explode("\n", file_get_contents($nearest_call["file"]));
$calling_code=$lines[$nearest_call["line"]-1];
$regex="/".$nearest_call["function"]."\\(([^\\)]+)\\)/";
preg_match_all($regex, $calling_code, $matches);
$args=preg_split("/\\s*,\\s*/", $matches[1][0]);
return $args[0];
}
function fn($argument) {
echo getFirstArgName();
}
$var1 = "foo";
$var2 = "bar";
fn($var1);
fn($var2);
?>
Output:
$var1$var2
Related
First, let me start by saying i'm a real beginner learning mostly PHP. Understanding the patterns and semantics of programming is more important to me than just learning the syntax. I did some research for what I'm going to ask, but I couldn't find any info about it. So, I was thinking... What if I need to do the following... Give a function multiple outputs to pass in other parts of the code. What is the name of this type of functionality (if it exists)? Or If it doesn't exist, why not? And what is the best practice to achieve the same semantic?
More details:
Let's say I want to call a function with one argument and return not only the value back to that same argument call location, but also in another location or into some other part of the program. Meaning a function with two outputs in two different locations, but the second location wouldn't be a call, just an output from the call made in the first location, returned at the same time with the same value output as the first. So, not calling it twice separately... But rather calling once and outputting twice in different locations. The second output would be used to pass the result into another part of the program and therefore wouldn't be appropriate as a "call/input", but more as an "output" only from the "input" value. How can I achieve multiple outputs in functions?
If this seems like a stupid question, I'm sorry. I couldn't find the info anywhere. Thanks in advance
What you want to do is basically this (i'll make it a 'practical' example):
function add($number1, $number2)
{
$result = $number1 + $number2;
return array('number1' => $number1,'number2' => $number2,'result' => $result);
}
$add = add(5,6); // Returns array('number1' => 5, 'number2' => 6, 'result' => 11);
You now have the two arguments and the result of that function at your disposal to use in other functions.
some_function1($add['result']);
...
some_function2($add['number1']);
If the question is about returning more than one variables, it is simply:
function wtf($foobar = true) {
$var1 = "first";
$var2 = "second";
if($foobar === true) {
return $var2;
}
return $var1;
}
You can either have the function return an array of values:
function foo($bar) {
$bat = 1;
return [$bar, $bat];
}
Or you can pass an argument that tells it which value to return:
function foo($bar, $return_bar=false) {
$bat = 1;
return $return_bar ? $bar : $bat;
}
I'm trying to return a value from a method as a reference in PHP5.3. I may be going at this the completely wrong way, but I am bringing an older project up to speed with some of the newer 5.3+ features.
Below is an example I whipped up to explain what is happening:
class Foo
{
static $foobar = 5;
function &bar()
{
return self::$foobar;
}
}
// Doesn't work
//$test1 = &call_user_func_array(array("Foo","bar"),array());
// Doesn't work
//$test1 = &call_user_func_array("Foo::bar",array());
// Doesn't work
//$f = new Foo; $test1 = &call_user_func_array(array($f,"bar"),array());
// WORKS
//$test1 = &Foo::bar();
//Doesn't work
//$function = "Foo::bar";
//$test1 = &$function();
// WORKS
$f = new Foo; $test1 = &$f->bar();
$test2 = Foo::bar();
var_dump($test1);
var_dump($test2);
$test1 = 10;
echo "----------<br />";
var_dump($test1);
var_dump($test2);
var_dump(Foo::bar()); //returns 10 when working, 5 when not working
The very last Foo::bar() should return a 10, since $test1 should be a reference to Foo::$foobar when everything works.
I realize that this example also uses some funky legacy PHP calling Foo::bar and the method bar() not being specified as static, but still being able to be invoked via ::
Any help would be greatly appreciated as the only fix I have so far is to just setup a switch on the argument list, and call the method directly based upon how many arguments exist.
This is just assigning $test1 to the value of $foobar (which is 5)
$test1 = &$f->bar();
This is just overwriting the value contained in $test1 with 10
$test1 = 10;
If you want to update the value within Foo, use
$f->foobar = 10;
Doesn't it already work in PHP 5.2.5: http://codepad.org/uMEIK210 (note the 10 as final result)?
I suppose, you would like to see the 10 three times.
For that (that $test2 is also a reference to the class field) you need to specify the & on both sides:
function &bar() and $test2 =& Foo::bar();
See the docs:
Note: Unlike parameter passing, here you have to use & in both places - to indicate that you want to return by reference, not a copy, and to indicate that reference binding, rather than usual assignment, should be done for $myValue.
So you just need to edit one line to get the (probably) desired 3 x 10:
$test2 =& Foo::bar();
Final hint
Do not use PHP references
First of all, try declaring the function static. Also the call should be a normal call. prefixed by ampersand as already answered.
class Foo
{
static $foobar = 5;
public static function &bar()
{
return self::$foobar;
}
}
The call:
$test1 =& Foo::bar();
Also, I can't see a valid reason for referencing a static variable. A static variable is a variable that doesn't change value between calls. It basically is a "global" var enclosed in a namespace. You only need read access from outside the class, the write should be done internally, as per the encapsulation principle. No need for the reference, really..
I have a function that searches for a string inside a text file. I want to use the same function to assign all lines to an array in case I am going to replace that string. So I will read the input file only once.
I have the search function working but I do not know how to deal with the array thing.
the code is something like that (I made the code sample much simpler,so please ignore the search function that actually isn't below)
function read_ini($config_file_name,$string){
$config_file = file($config_file_name);
foreach($config_file as $line) {
return_string = trim(substr($line,0,15));
$some_global_array = $line'
}
}
echo read_ini('config.ini','database.db')
if ($replaced) {file_put_contents('config.ini', $some_global_array);}
http://php.net/parse_ini_file
I know it doesn't answer the question, but it quite possibly removes the need for even having to ask.
The deal with globals, though, is that they must be defined at the top of the function as globals, or else they're considered part of the function's scope.
function write_global() {
global $foo;
$foo = 'bar';
}
write_global();
echo $foo; // bar
Anyone has an idea if this is at all possible with PHP?
function foo($var) {
// the code here should output the value of the variable
// and the name the variable has when calling this function
}
$hello = "World";
foo($hello);
Would give me this output
varName = $hello
varValue = World
EDIT
Since most people here 'accuse' me of bad practices and global variables stuff i'm going to elaborate a little further on why we are looking for this behaviour.
the reason we are looking at this kind of behaviour is that we want to make assigning variables to our Views easier.
Most of the time we are doing this to assign variables to our view
$this->view->assign('products', $products);
$this->view->assign('members', $members);
While it would be easier and more readable to just be able to do the following and let the view be responsible to determining the variable name the assigned data gets in our views.
$this->view->assign($products);
$this->view->assign($members);
Short answer: impossible.
Long answer: you could dig through apd, bytekit, runkit, the Reflection API and debug_backtrace to see if any obscure combination would allow you to achieve this behavior.
However, the easiest way is to simply pass the variable name along with the actual variable, like you already do. It's short, it's easy to grasp, it's flexible when you need the variable to have a different name and it is way faster than any possible code that might be able to achieve the other desired behavior.
Keep it simple
removed irrelevant parts after OP edited the question
Regardless of my doubt that this is even possible, I think that forcing a programmer on how to name his variables is generally a bad idea. You will have to answer questions like
Why can't I name my variable $arrProducts instead of $products ?
You would also get into serious trouble if you want to put the return value of a function into the view. Imagine the following code in which (for whatever reason) the category needs to be lowercase:
$this->view->assign(strtolower($category));
This would not work with what you're planning.
My answer therefore: Stick to the 'verbose' way you're working, it is a lot easier to read and maintain.
If you can't live with that, you could still add a magic function to the view:
public function __set($name, $value) {
$this->assign($name, $value);
}
Then you can write
$this->view->product = $product;
I don't think there is any language where this is possible. That's simply not how variables work. There is a difference between a variable and the value it holds. Inside the function foo, you have the value, but the variable that held the value is not available. Instead, you have a new variable $var to hold that value.
Look at it like this: a variable is like a bucket with a name on it. The content (value) of the variable is what's inside the bucket. When you call a function, it comes with its own buckets (parameter names), and you pour the content of your bucket into those (well, the metaphor breaks down here because the value is copied and still available outside). Inside the function, there is no way to know about the bucket that used to hold the content.
What you're asking isn't possible. Even if it was, it would likely be considered bad practice as its the sort of thing that could easily get exploited.
If you're determined to achieve something like this, the closest you can get would be to pass the variable name as a string and reference it in the function from the $GLOBALS array.
eg
function this_aint_a_good_idea_really($var) {
print "Variable name: {$var}\n";
print "Variable contents: {$GLOBALS[$var]}\n";
}
$hello="World";
this_aint_a_good_idea_really('hello');
But as I say, that isn't really a good idea, nor is it very useful. (Frankly, almost any time you resort to using global variables, you're probably doing something wrong)
Its not impossible, you can find where a function was invoked from debug_backtrace() then tokenize a copy of the running script to extract the parameter expressions (what if the calling line is foo("hello $user, " . $indirect($user,5))?),
however whatever reason you have for trying to achieve this - its the wrong reason.
C.
Okay, time for some ugly hacks, but this is what I've got so far, I'll try to work on it a little later
<?php
class foo
{
//Public so we can test it later
public $bar;
function foo()
{
//Init the array
$this->bar = array();
}
function assign($__baz)
{
//Try to figure out the context
$context = debug_backtrace();
//assign the local array with the name and the value
//Alternately you can initialize the variable localy
//using $$__baz = $context[1]['object']->$__baz;
$this->bar[$__baz] = $context[1]['object']->$__baz;
}
}
//We need to have a calling context of a class in order for this to work
class a
{
function a()
{
}
function foobar()
{
$s = "testing";
$w = new foo();
//Reassign local variables to the class
foreach(get_defined_vars() as $name => $val)
{
$this->$name = $val;
}
//Assign the variable
$w->assign('s');
//test it
echo $w->bar['s'];
}
}
//Testrun
$a = new a();
$a->foobar();
impossible - the max. ammount of information you can get is what you see when dumping
debug_backtrace();
Maybe what you want to do is the other way around, a hackish solution like this works fine:
<?php
function assign($val)
{
global $$val;
echo $$val;
}
$hello = "Some value";
assign('hello');
Ouputs: Some value
What you wish to do, PHP does not intend for. There is no conventional way to accomplish this. In fact, only quite extravagant solutions are available. One that remains as close to PHP as I can think of is creating a new class.
You could call it NamedVariable, or something, and as its constructor it takes the variable name and the value. You'd initiate it as $products = new NamedVariable('products', $productData); then use it as $this->view->assign($products);. Of course, your declaration line is now quite long, you're involving yet another - and quite obscure - class into your code base, and now the assign method has to know about NamedVariable to extract both the variable name and value.
As most other members have answered, you are better off suffering through this slight lack of syntactic sugar. Mind you, another approach would be to create a script that recognizes instances of assign()'s and rewrites the source code. This would now involve some extra step before you ran your code, though, and for PHP that's silly. You might even configure your IDE to automatically populate the assign()'s. Whatever you choose, PHP natively intends no solution.
This solution uses the GLOBALS variable. To solve scope issues, the variable is passed by reference, and the value modified to be unique.
function get_var_name(&$var, $scope=FALSE) {
if($scope) $vals = $scope;
else $vals = $GLOBALS;
$old = $var;
$var = $new = 'unique'.rand().'value';
$vname = FALSE;
foreach ($vals as $key => $val) {
if($val === $new) $vname = $key;
}
$var = $old;
return $vname;
}
$testvar = "name";
echo get_var_name($testvar); // "testvar"
function testfunction() {
$var_in_function = "variable value";
return get_var_name($var_in_function, get_defined_vars());
}
echo testfunction(); // "var_in_function"
class testclass {
public $testproperty;
public function __constructor() {
$this->testproperty = "property value";
}
}
$testobj = new testclass();
echo get_var_name($testobj->testproperty, $testobj); // "testproperty"
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 :)
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.
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.
Nope, not possible. Sorry.
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 $a and strip out the leading 0.
Addendum: Only do this if you are
Never showing this code to anyone
Never need to change or maintain this code
Are crazy
Not doing this for a job
Look, just never do this, it is a joke
I know this is very very late, but i did it in a different way.
It might honestly be a bit bad for performance, but since it's for debugging it shouldn't be a problem.
I read the file where the function is called, on the line it was called and I cut out the variable name.
function dump($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>';
}
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 $_GLOBALS (if it were a global for some reason) and loop through that to find something which matches the value of your variable. This is a very hacky and not very reliable method though. Your original method is the most efficient way.
No, the closer you will get is with get_defined_vars().
EDIT: I was wrong, after reading the user comments on get_defined_vars() it's possible with a little hack:
function ev($variable){
foreach($GLOBALS as $key => $value){
if($variable===$value){
echo '<p>$'.$key.' - '.$value.'</p>';
}
}
}
$lol = 123;
ev($lol); // $lol - 123
Only works for unique variable contents though.
Bit late to the game here, but Mach 13 has an interesting solution: How to get a variable name as a string in PHP
You could use eval:
function debug($variablename)
{
echo ($variablename . ":<br/>");
eval("global $". $variablename . ";");
eval("var_dump($" . $variablename . ");");
}
Usage: debug("myvar") not debug($myvar)
This is late post but I think it is possible now using compact method
so the code would be
$a=1;
$b=2;
$c=3
var_dump(compact('a','b','c'));
the output would be
array (size=3)
'a' => int 1
'b' => int 2
'c' => int 3
where variable name a, b and c are the key
Hope this helps
I believe Alix and nickf are suggesting this:
function debug($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)