用户自定义函数

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一个函数可由以下的语法来定义：

Example #1 展示函数用途的伪代码

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

任何有效的 PHP 代码都有可能出现在函数内部，甚至包括其它函数和类定义。

函数名和 PHP 中的其它标识符命名规则相同。有效的函数名以字母或下划线打头，后面跟字母，数字或下划线。可以用正则表达式表示为：[a-zA-Z_\x7f-\xff][a-zA-Z0-9_\x7f-\xff]*。

Tip

请参见用户空间命名指南。

函数无需在调用之前被定义，除非是下面两个例子中函数是有条件被定义时。

当一个函数是有条件被定义时，必须在调用函数之前定义。

Example #2 有条件的函数

  <?php

$makefoo  =  true ;

 /* 不能在此处调用foo()函数，
   因为它还不存在，但可以调用bar()函数。*/

 bar ();

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

 /* 现在可以安全调用函数 foo()了，
   因为 $makefoo 值为真 */

 if ( $makefoo )  foo ();

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

 ?>

Example #3 函数中的函数

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

 /* 现在还不能调用bar()函数，因为它还不存在 */

 foo ();

 /* 现在可以调用bar()函数了，因为foo()函数
   的执行使得bar()函数变为已定义的函数 */

 bar ();

 ?>

PHP 中的所有函数和类都具有全局作用域，可以定义在一个函数之内而在之外调用，反之亦然。

PHP 不支持函数重载，也不可能取消定义或者重定义已声明的函数。

Note: 函数名是大小写无关的，不过在调用函数的时候，使用其在定义时相同的形式是个好习惯。

PHP 的函数支持可变数量的参数和默认参数。参见 func_num_args() ， func_get_arg() 和 func_get_args() 。

在 PHP 中可以调用递归函数。

Example #4 递归函数

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

Note: 但是要避免递归函数／方法调用超过 100-200 层，因为可能会使堆栈崩溃从而使当前脚本终止。无限递归可视为编程错误。

用户评论:

[#1] Muneeb Aslam [2015-11-23 15:09:12]

following is a function that can be used to convert numeric date to alphabetic date, e-g from 2015-11-16 to 16 Nov, 2015.

1. Function takes 3 parameters, numeric date, locale and length of month
2. Function currently supports EN and ES month names.
3. Function can be calles as <?php convertDate("2015-11-16","en","full"); ?>

<?php function convertDate($date,$locale,$length){ $monthNames = array( "en" => array( "full" => array(1=>'January','February','March','April','May', 'June','July','August','September','October','November','December'), "short" => array(1=>'Jan','Feb','Mar','Apr','May','Jun', 'Jul','Aug','Sep','Oct','Nov','Dec') ), "es" => array( "full" => array(1=>'Enero','Febrero','Marzo','Abril','Mayo', 'Junio','Julio','Agosto','Septiembre','Octubre','Noviembre','Deciembre'), "short" => array(1=>'Ene','Feb','Mar','Abr','May','Jun', 'Jul','Ago','Sep','Oct','Nov','Dec') ), ); $exploded = explode("-",$date); $year = $exploded[0]; $month = $exploded[1]; $day = $exploded[2]; $month = $monthNames[$locale][$length][$month]; $date = $day . " " . $month . ", " . $year; return $date; } ?>

[#2] ohcc at 163 dot com [2015-11-07 15:52:14]

As of PHP 7.0, you can restrain type of return value of user defined functions.

Syntax is : function FunctionName ($arg1, $arg2, ...) : TYPE { ... }

TYPE is a string representing the type of return value, TYPE can be a class name or a php variable type, such as array/string/bool/int/float.

When TYPE is one of the following value, it also stands for a classname

str/boolean/integer/real/double/resource/object/scalar

However,in my opion, boolean/bool, integer/int ... should have the same meaning, but at least in PHP7, they stand for different meanings respectively. This may be fixed in later versions of PHP.

<?php function wxc ($var) : string { return $var; } ?>

this function must return a string, if it return something else when called, a "Fatal error: Uncaught TypeError" error will be triggered.

code above is supported only in PHP 7+

[#3] N Atanackovic [2015-03-16 17:31:16]

You can also call function from itself.  For example, I want to reach the deepest value in multidimensional array and I call function from inside the very same function. In this example function behave as some meta-loop.

<?php $arr1=array('a'=>array('e'=>array('f'=>array('g'=>'h', 'n' )),'b','c')); $arr2=array('a'=>array('e'=>array('f'=>array('g'=>array('l'=>array('m'=>'w','q')), 'n' )),'b','c')); function Deep($array){     foreach($array as $key){         if(is_array($key)){              return Deep($key);//calling the function inside the function }else { echo $key;         }     } } echo Deep($arr1); //outputs: hn echo Deep($arr2); //outputs: wq ?>

[#4] php at xenhideout dot nl [2014-09-15 17:59:28]

Please be advised that the code block defining the function, within the function_exists() call, has to be executed for the function to get defined, whereas this is not the case for regular, unenclosed functions.

Meaning, if you write code like this:

<?php do_function(); if (!function_exists('my_undefined')) { function my_undefined() { } } function do_function() { my_undefined(); } ?>

..Then my_undefined will not be defined before the code in do_function calls it. Some people put their function sections below the regular executing code of the script. Making any of it 'pluggable' can then cause problems.

[#5] aydinantmen [at] hotmail [dot] com [2014-04-23 17:17:23]

I want to use multidimentional arrays in a callback function what accepts second parameter.

Solution:

<?php $arr1 = array("a" => "b", "c", "d's", "e" => array("f's", "g" => array("h's", "i" => "j's"))); $arr2 = mdarr_parameter($arr1); $arr3 = mdarr_parameter($arr2, true); function mdarr_parameter($needle, $job=false) { if (is_array($needle)) { foreach($needle as $name => $value) { $needle[$name] = mdarr_parameter($value, $job); } } else { // Now you do anything you want... if ($job === true) { $needle = stripslashes($needle); } else { $needle = addslashes($needle); } } return $needle; } print_r($arr2); print_r($arr3); /** Outputs: Array ( [a] => b [0] => c [1] => d\'s [e] => Array ( [0] => f\'s [g] => Array ( [0] => h\'s [i] => j\'s ) ) ) Array ( [a] => b [0] => c [1] => d's [e] => Array ( [0] => f's [g] => Array ( [0] => h's [i] => j's ) ) ) **/ ?>