Straightforward:
I want to write some code which tells if a variable was passed by reference or not.
For example:
<?php
function isReference($variable) {
//return TRUE if &$something was passed
//return FALSE if $something was passed
}
$text = 'Anything';
$a = isReference(&$text); //return TRUE
$b = isReference($test); //return FALSE
?>
For those who are curious - why do I need it?
Firstly I do not like to leave problems unsolved.
Secondly, I am currently enhancing by skills by writing an extension to mysqli, which would prepare statements similar to how PDO does. If anybody knows the difference between bindParam and bindValue in PDO, they know that it's a workaround of this question. I can just make two functions, but I wonder if it's possible with one.
Thanks in advance.
Here's a way to do it without using the debug_zval_dump function:
function isReference($variable) {
$variable = array($variable);
$arg = func_get_arg(0);
$isRef = isset($arg[0]) && $arg === array($variable[0]);
$variable = $variable[0];
return $isRef;
}
Note: there is only a single case when this will not work:
$text = array(&$text); // although i don't see why such a structure could be used
isReference($text); // will wrongly return false
Obviously you can bypass this limitation by using a random unique key (instead of 0).
You can use debug_zval_dump to dump a string representation of an internal zend value to output:
function isRef(&$val) {
ob_start();
debug_zval_dump(&$val);
$ret = ob_get_clean();
preg_match('~refcount\((\d+)\)~', $ret, $matches);
return $matches[1] - 4;
}
$var1 = 'Var1';
$var2 = &$var1; // passed by ref
if(isRef($var2)) echo 'Passed by ref';
But be aware of PHP - 5.4.
Simply checking for the default value seems to work fine in my tests. Obviously it wont work if $t is already set to 'x' but you could change the default value to something totally unlikely to workaround this:
function test(&$t='x'){
if($t!='x') $t = 2;
}
test(); echo $t; //outputs: null
test($t); echo $t; //outputs: 2
Related
I'm trying to write a function that will take any number of arguments, and will return the first argument, in order, that is valid (in my case !empty).
I've been able to pretty much get it working how I want, except I'm getting some notices because of undefined variables. See below for examples:
function cascade()
{
if (func_num_args() < 1) return false;
foreach (func_get_args() as &$arg) {
if (!empty($arg)) return $arg;
}
return false;
}
You can see that I've tried to declare that each $arg of the foreach is passed by reference, but that doesn't seem to have done the trick.
To elaborate on how I plan to use this function, see below:
$a = 'a';
$c = 'c';
echo cascade($z, $b, $a, $c);
Since $z and $b are undefined, the first non-empty variable in the list is $a so the output is a as expected. However, you then get the undefined variable notices, which I wish to get rid of.
I realise I can just say echo #cascade($z, $b, $a, $c); which would suppress the errors, but I want to know if there is a way around this issue, so that the reference can be passed somehow. Any thoughts?
Edit:
To further highlight what I'm trying to acheive, see the following function that DOES work without throwing errors, even when passed an undefined variable:
// returns default value if input variable is not set
function ifset(&$var, $default = false) {
return isset($var) ? $var : $default;
}
With this function, if param 1 is not set, then the default value in param 2 is returned. Either way, no error is thrown.
What I am trying to achieve is the same result, but with ANY number of arguments, as this function is limited to 1, unless I nest them (gets messy).
A real life example:
This is WHY I want this function and how I would use it in a real life scenario:
<input type="text" name="customerName" value="<?= cascade($order->fullName, $currentUser->fullName, 'Anonymous') ?>">
So if we have an order in the making, and there is a name available from that, we use that, if that info hasn't been saved yet, we use the logged in user's name as the default value, if no one is logged in, we use 'Anonymous'.
Not exactly what I would do in real life, but perhaps it highlights example usage?
For those who are suggesting defining the variables to mitigate the errors, the who point of this function is to work though a chain of values, giving priority to the ones that come first, then moving to the next if that is 'empty' and so on, until eventually a FALSE default value is returned if all are empty.
The Notice you're seeing is triggered at the function call, not inside the function itself. Therefore, there is nothing you can do inside the function to solve the problem. However, there are a number of ways of solving this problem depending on how your variables are prepared before the function call.
Solution #1: Define the variables before the function call.
for instance:
$z = ''; OR $z = null;
or any falsy value like : null, "", 0, "0", 0.0, [], ..., your function will still work as expected and you won't see the notice.
Solution #2: Test for validity before the function call.
if( !isset($z) ){ $z = ''; }
echo cascade($z);
Solution #3: Test for validity as part of the function call.
This is the same thing as solution #2 but a bit more elegant. Use the Ternary function to pass the variable value or an empty string depending on whether or not the variable is set.
echo cascade(
isset($z)?$z:'',
isset($b)?$b:'',
isset($a)?$a:'',
isset($c)?$c:''
);
Solution #4: If using PHP 7 or above, you can use the new Null Coalescing Operator. This is the same thing as solution #3, but more elegant still.
echo cascade($z ?? '', $b ?? '', $a ?? '', $c ?? '');
If you want a clean alternative to your function, you can try this:
function cascade()
{
$args = func_get_args();
while (!($arg = array_shift($args)));
return $arg ? $arg : false;
}
BIG THANKYOU to JBH for Editing significantly this answer.
The undefined variable notice is not from the code in function but it is from the function call cascade($z, $b, $a, $c)
You are passing undefined variables ($z and $b) as arguments to the function. Since they are not defined any where in the code, you are getting notice.
To get rid of the the notices, define the variables before passing them as arguments.
$a = 'a';
$c = 'c';
$z = '';
$b = '';
echo cascade($z, $b, $a, $c);
OR
echo cascade('', '', $a, $c);
Don't know if this is "good enough".
Create an array of the variables and use array filter to remove the null values.
Use array values to reset the keys.
Now $arr[0] is the first non empty item.
https://3v4l.org/PlmrS
$a = 'a';
$c = 'c';
$arr =array_values(array_filter([$z, $b, $a, $c]));
Var_dump($arr);
Thank you for all your kind answers, but unfortunately none of them solved my problem. Perhaps I didn't explain it well enough, or I over-complicated it with too much information confusing the issue, but anyway I've been able to find the answer.
The following function does exactly what I wanted. It uses the variadic syntax (php 5.6 and over) which allows a variable number of arguments, all of which are passed by reference.
function cascade(&...$args)
{
if (count($args) < 1) return false;
foreach ($args as &$arg) {
if (!empty($arg)) return $arg;
}
return false;
}
I have this line in a class function:
$this_value = eval("return $$existing_value;");
This gives me the value I need when the $$existing_value variable is set in the function, but I've found that I actually need to access the global scope in 99% of cases. I've tried rewritting it as $this_value = eval("return global $$existing_value;");, but that returns a php error.
Does any know how I can do this correctly?
(by the way, I am aware of the poor pratice this represents - but given the situation I cannot think of any other approaches)
Try
$this_value = eval('global $existing_value; return $$existing_value;');
or
$this_value = eval('global $$existing_value; return $$existing_value;');
$x = 3;
function sss()
{
$x = 1;
$y = eval('global $x; return $x;');
var_dump($y);
}
sss();
Will output int(3) , so it works , but be carefull about double quotes and simple quotes!
Since eval is returning the value you need, you should be bale to just assign the return value to the $_GLOBAL or $_SESSION (preferred because $_GLOBAL is evil) super globals.
$foo['bar'] = "pie";
$fixed_name_variable = "foo['bar']";
$_GLOBAL['foo'] = eval("return $$fixed_name_variable;");
echo $_GLOBAL['foo']; // pie
I've been re-thinking this process. I have relised that I can add a new array with a fixed name which the various processes contributing to this function can add the values needed, programatically, rather than trying to guess at names.
It'll also be far more secure and reliable than variable variables.
Is there a function in PHP to set default value of a variable if it is not set ?
Some inbuilt function to replace something like:
$myFruit = isset($_REQUEST['myfruit']) ? $_REQUEST['myfruit'] : "apple" ;
PHP kind of has an operator for this (since 5.3 I think) which would compress your example to:
$myFruit = $_REQUEST['myfruit'] ?: "apple";
However, I say "kind of" because it only tests if the first operand evaluates to false, and won't suppress notices if it isn't set. So if (as in your example) it might not be set then your original code is best.
The function analogous to dictionary.get is trivial:
function dget($dict, $key, $default) {
return isset($dict[$key]) ? $dict[$key] : $default;
}
For clarity, I'd still use your original code.
Edit: The userland implementation #2 of ifsetor() at http://wiki.php.net/rfc/ifsetor is a bit neater than the above function and works with non-arrays too, but has the same caveat that the default expression will always be evaluated even if it's not used:
function ifsetor(&$variable, $default = null) {
if (isset($variable)) {
$tmp = $variable;
} else {
$tmp = $default;
}
return $tmp;
}
As far as i know there exists nothing like this in PHP.
You may implement something like this yourself like
$myVar = "Using a variable as a default value!";
function myFunction($myArgument=null) {
if($myArgument===null)
$myArgument = $GLOBALS["myVar"];
echo $myArgument;
}
// Outputs "Hello World!":
myFunction("Hello World!");
// Outputs "Using a variable as a default value!":
myFunction();
// Outputs the same again:
myFunction(null);
// Outputs "Changing the variable affects the function!":
$myVar = "Changing the variable affects the function!";
myFunction();
You could also create a class implementing the ArrayAccess, which you pass 2 arrays during construction ($_REQUEST and an array with defaults) and make it choose the default value transparently.
Btw., relying on $_REQUEST is not a wise idea. See the manual on $_REQUEST for further information.
Instead of testing, if a key not exists and then return a default value, you can also fill your array with this values, before accessing it.
$expectedKeys = array('myfruit');
$requestData = array_merge (
array_combine(
$expectedKeys,
array_fill(0, count($expectedKeys), null)),
$_REQUEST);
$postData is now an array with all keys you expect (specified by $expectedKeys), but any entry, that is missing in $_REQUEST is null.
$myFruit = $requestData['myfruit'];
if (is_null($myFruit)) {
// Value not exists
}
But I also recommend to just stay with the ternary operator ?:.
There is a function called ife() in the CakePHP framework, you can find it here http://api13.cakephp.org/view_source/basics.php/, it is the last function!
You can use it like this:
echo ife($variable, $variable, 'default');
When passing a non-existent value by reference, PHP creates the value and sets it to NULL. I noticed it when memory increases were occurring while checking empty values in some functions. Take the following function:
function v(&$v,$d=NULL){return isset($v)?$v:$d;}
$bar = v($foo, $default);
This would be shorthand for:
if(isset($foo))
{
$bar = $foo;
}
else
{
$bar = $default;
}
However, when passing non-existent variables PHP creates them. In the case of variables - they are removed as soon as the method/function ends - but for checking super global arrays like $_GET or $_POST the array element is never removed causing extra memory usage.
$request_with = v($_SERVER['HTTP_X_REQUESTED_WITH']);
Can anyone explain why this happens and if it is a PHP todo fix or a feature for some other crazy use of values?
XeonCross' function v is a shorthand for the often used:
$val= isset($arr['elm']) ? $arr['elm'] : 'default'
to avoid the dreaded 'Undefined index: elm' notice. A nice helper function would be:
function ifset(&$v1, $v2 = null) {
return isset($v1) ? $v1 : $v2;
}
as Xeoncross suggested, so you could write the much nicer
$val = ifset($arr['elm'],'default')
however, this has a lot of interesting (?) quirks in our beloved "language" that we call PHP:
inside the function ifset, $v1 seems UNSET, so it correctly returns the value $v2 and you might conclude that ifset works ok. But afterwards $arr['elm'] is silently set to NULL. So consider the following:
function wtf(&$v) {
if (isset($v))
echo "It is set";
else
echo "It is NOT set";
}
$p=[];
wtf($p['notexist']); => It is NOT set
$p; => [ 'notexist' => NULL ]
But this is another delusion, as the isset() function returns false for NULL values as well:
$x=NULL;
isset($x) => false... huh??
Did we expect this? well.. it is in the documentation, so this is by design as well. Welcome to the wonderful world of php.
The reason you have the memory leak, is because you're telling it to.
When you ask for a reference parameter, PHP will provide you with one. When you are calling a function with an unset variable, PHP will set the variable and then pass the reference to that new variable. When you call it with a superglobal, it creates the missing index. That's because you told it to.
However, I must ask why specifically do you need variable references? 99.9% of the time you don't really need them. I suspect that it'll work just fine to do:
function v($v, $d = null) { return isset($v) ? $v : $d; }
Or, if you really must use references (which you can't get around your original problem with), you should also return a reference:
function &v(&$v, $d = null) {
if (isset($v)) {
return $v;
}
return $d;
}
Otherwise it's pointless to take a reference and not return one...
I'm using a template engine that inserts code in my site where I want it.
I wrote a function to test for something which is quite easy:
myfunction() { return '($this->data["a"]["b"] ? true : false)'; }
The problem is, $this->data is private, and I can't access it everywhere, so I have to use getData(); which causes my problem.
$this->getData()['a']['b']
does not work, and assigning the value first doesn't either because it will be used directly in an if() block.
Any ideas?
Since PHP 5.4 it's possible to do exactly that:
getSomeArray()[2]
Reference: https://secure.php.net/manual/en/language.types.array.php#example-62
On PHP 5.3 or earlier, you'll need to use a temporary variable.
You cannot use something like this :
$this->getData()['a']['b']
ie, array-access syntax is not possible directly on a function-call.
Youy have to use some temporary variable, like this :
$tmp = $this->getData();
$tmp['a']['b'] // use $tmp, now
In your case, this probably means using something like this :
function myfunction() {
$tmp = $this->getData();
return ($tmp['a']['b'] ? true : false);
}
You have to :
first, call your getData() method, and store its return value in a temporary varibale
then, use that temporary variable for your test
You don't have much choice about that, actually...
Ok... apparently there really isn't a better way, so I'm going to answer myself with a not so beautiful solution:
I created the function:
arrayGet($array, $index) { return $array[$index]; }
And used it like this:
myfunction() { return '(arrayGet(arrayGet($this, "a"), "b") ? true : false)' }
This is not pretty but works.
$this->data is always accessible, if it is protected. $object->data is not accessible from everywhere, so if you're returning $this in your code, and it is evaluated as such, it should be ok.
Btw, there is a bug in your code: The quotes need to be escaped.
myfunction() { return '($this->data[\'a\'][\'b\'] ? true : false)'; }
It is possible from PHP version 5.4.
If you don't want a temporary variable for that and your PHP version is less, than 5.4, than you still can use a few built in functions to get the first or the last element:
$x = 'first?last';
$first = array_shift(explode('?', $x));
$last = end(explode('?', $x));
$last2 = array_pop(explode('?', $x));
Edit:
!!! Please note, that in later versions( 5.4+ ) PHP will throw a notice, because end only expects variables as parameter.