CODEWITHSUNDEEP
php
Tal
Tal

Reputation: 181

References in PHP

I know that using & before a function's parameter means it's passed by reference, and can be used for output, but what does it mean if I use it in another context?

For example:

function foo (&$param) {
    $param = 3;
}

foo (&$a);
echo $a;

I added the & when calling foo just to see what happens, and it didn't actually appear to change anything, and $a isn't even defined before that point.

Could anyone please explain that?

Upvotes: 0

Views: 706

Answers (3)

Fluffeh
Fluffeh

Reputation: 33502

When you use &$param in a function it mean you pass by reference. You however shouldn't use it in the function call - with current versions of PHP, this will generate a warning. Function calls are only allowed to pass a variable now. The function declaration must be indicative of whether the function accepts the argument by reference or by passing.

Pass it as per the docs functionName($variableName); rather than functionName(&$variableName)

A function called with an &$ parameter will now generate a warning, which can be suppressed, but is still a depreciated way to call.

Upvotes: 3

WatsMyName
WatsMyName

Reputation: 4478

Well consider a code below, This may not answer your question but a good example to understand the referenced variable. 

<?
$variable="this is some test";

$refvariable = &$variable;
$nvariable = $variable;
$variable ="This IS ANOTHER VARIABLE STRING";

echo "Referenced Variable=".$refvariable;
echo "<bR>Normal Variable=".$nvariable;

?> In simple words, above $nvariable is the normal variable, when its echoed it takes the value of $variable set initially. Now consider $refvariable which is referenced variable, it takes the latest value of $variable. Hope above example help you understand.

Upvotes: 0

DaveRandom
DaveRandom

Reputation: 88647

The manual says:

Note: There is no reference sign on a function call - only on function definitions. Function definitions alone are enough to correctly pass the argument by reference. As of PHP 5.3.0, you will get a warning saying that "call-time pass-by-reference" is deprecated when you use & in foo(&$a);.

Further to this, as of 5.4.0 you will actually get a parse error. Before that it will work but since 5.3 it will complain about. Since there are some native functions that actually require call-time pass-by-reference (for example debug_zval_dump() and underneath call_user_func() and call_user_func_array()) this aspect of 5.4 degrades badly.

Upvotes: 7

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