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Passing by Reference

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You can pass a variable by reference to a function so the function can modify the variable. The syntax is as follows:

<?php
function foo(&$var)
{
    $var++;
}

$a=5;
foo($a);
// $a is 6 here
?>

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);. And as of PHP 5.4.0, call-time pass-by-reference was removed, so using it will raise a fatal error.

The following things can be passed by reference:

  • Variables, i.e. foo($a)

  • References returned from functions, i.e.:

    <?php
    function foo(&$var)
    {
            $var++;
    }
    function &    bar()
    {
            $a = 5;
        return     $a;
    }
    foo(bar());
    ?>
    See more about returning by reference.

No other expressions should be passed by reference, as the result is undefined. For example, the following examples of passing by reference are invalid:

<?php
function foo(&$var)
{
    $var++;
}
function bar() // Note the missing &
{
    $a = 5;
    return $a;
}
foo(bar()); // Produces fatal error as of PHP 5.0.5, strict standards notice
            // as of PHP 5.1.1, and notice as of PHP 7.0.0

foo($a = 5); // Expression, not variable
foo(5); // Produces fatal error

class Foobar
{
}

foo(new Foobar()) // Produces a notice as of PHP 7.0.7
                  // Notice: Only variables should be passed by reference
?>

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Document created the 30/01/2003, last modified the 26/10/2018
Source of the printed document:https://www.gaudry.be/en/php-rf-language.references.pass.html

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References

  1. View the html document Language of the document:fr Manuel PHP : http://php.net

These references and links indicate documents consulted during the writing of this page, or which may provide additional information, but the authors of these sources can not be held responsible for the content of this page.
The author This site is solely responsible for the way in which the various concepts, and the freedoms that are taken with the reference works, are presented here. Remember that you must cross multiple source information to reduce the risk of errors.

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