User-defined functions

A function is defined using the  keyword,
a name, a list of parameters (which might be empty) seperated by commas
() enclosed in parentheses, followed by the body of
the function enclosed in curly braces, such as the following:

function``,

**Voorbeeld: Declaring a new function named **

<?php
function foo($arg_1, $arg_2, /* ..., */ $arg_n)
{
    echo "Example function.\n";
    return $retval;
}
?>

Opmerking: > As of PHP 8.0.0, the list of parameters may have a trailing comma:
```php

Any valid PHP code may appear inside the body of a function, even other
functions and 
definitions.

class

Function names follow the same rules as other labels in PHP. A
valid function name starts with a letter or underscore, followed
by any number of letters, numbers, or underscores. As a regular
expression, it would be expressed thus:
.

^[a-zA-Z_\x80-\xff][a-zA-Z0-9_\x80-\xff]*$

Functions need not be defined before they are referenced,
 when a function is conditionally defined as
shown in the two examples below.

except

When a function is defined in a conditional manner such as the two
examples shown. Its definition must be processed 
to being called.

prior

Voorbeeld: Conditional functions

<?php

$makefoo = true;

/* We can't call foo() from here 
   since it doesn't exist yet,
   but we can call bar() */

bar();

if ($makefoo) {
  function foo()
  {
    echo "I don't exist until program execution reaches me.\n";
  }
}

/* Now we can safely call foo()
   since $makefoo evaluated to true */

if ($makefoo) foo();

function bar() 
{
  echo "I exist immediately upon program start.\n";
}

?>

Voorbeeld: Functions within functions

<?php
function foo() 
{
  function bar() 
  {
    echo "I don't exist until foo() is called.\n";
  }
}

/* We can't call bar() yet
   since it doesn't exist. */

foo();

/* Now we can call bar(),
   foo()'s processing has
   made it accessible. */

bar();

?>

All functions and classes in PHP have the global scope - they can be called outside a function even if they were defined inside and vice versa.

PHP does not support function overloading, nor is it possible to undefine or redefine previously-declared functions.

Opmerking: > Function names are case-insensitive for the ASCII characters to , though it is usually good form to call functions as they appear in their declaration. A``Z

Both  and  are supported in functions. See also the function
references for
,
, and
 for more information.

variable number of argumentsdefault argumentsfunc_num_args``func_get_arg``func_get_args

It is possible to call recursive functions in PHP.

Voorbeeld: Recursive functions

<?php
function recursion($a)
{
    if ($a < 20) {
        echo "$a\n";
        recursion($a + 1);
    }
}
?>

Opmerking: > Recursive function/method calls with over 100-200 recursion levels can smash the stack and cause a termination of the current script. Especially, infinite recursion is considered a programming error.

Volgende Function parameters and arguments →

User-defined functions

User-defined functions

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