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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]*。
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 ( $a + 1 );
}
}
?>
Note: 但是要避免递归函数/方法调用超过 100-200 层,因为可能会使堆栈崩溃从而使当前脚本终止。 无限递归可视为编程错误。
[#1] Muneeb Aslam [2015-11-23 15:09:12]
following is a function that can be used to convert numeric date to alphabetic date, e-g from 2015-11-16 to 16 Nov, 2015.
1. Function takes 3 parameters, numeric date, locale and length of month
2. Function currently supports EN and ES month names.
3. Function can be calles as
<?php convertDate("2015-11-16","en","full"); ?>
<?php
function convertDate($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
)
)
)
**/
?>