(PHP 4, PHP 5, PHP 7, PHP 8)
func_get_arg — 返回参数列表的某一项
从用户自定义函数的参数列表中获取某个指定的参数。
该函数可以配合 func_get_args() 和 func_num_args() 一起使用，从而使得用户自定义函数可以接受自定义个数的参数列表。
position参数的偏移量。函数的参数是从 0 开始计数的。
返回指定的参数，错误则返回 false。
当在自定义函数的外面调用的该函数的时候会发出一个警告，
或者是当 position 比实际传入的参数的数目大的时候也会发出一个警告。
示例 #1 func_get_arg() 例子
<?php
function foo()
{
$numargs = func_num_args();
echo "Number of arguments: $numargs\n";
if ($numargs >= 2) {
echo "Second argument is: " . func_get_arg(1) . "\n";
}
}
foo(1, 2, 3);
?>以上示例会输出：
Number of arguments: 3 Second argument is: 2
示例 #2 byRef 和 byVal 参数的 func_get_arg() 示例
<?php
function byVal($arg) {
echo 'As passed : ', var_export(func_get_arg(0)), PHP_EOL;
$arg = 'baz';
echo 'After change : ', var_export(func_get_arg(0)), PHP_EOL;
}
function byRef(&$arg) {
echo 'As passed : ', var_export(func_get_arg(0)), PHP_EOL;
$arg = 'baz';
echo 'After change : ', var_export(func_get_arg(0)), PHP_EOL;
}
$arg = 'bar';
byVal($arg);
byRef($arg);
?>以上示例会输出：
注意:
As of PHP 8.0.0, the func_*() family of functions is intended to be mostly transparent with regard to named arguments, by treating the arguments as if they were all passed positionally, and missing arguments are replaced with their defaults. This function ignores the collection of unknown named variadic arguments. Unknown named arguments which are collected can only be accessed through the variadic parameter.
注意:
如果参数以引用方式传递，函数对该参数的任何改变将在函数返回后保留。As of PHP 7 the current values will also be returned if the arguments are passed by value.
注意: 此函数仅返回传递参数的副本，不会考虑默认（未传递）参数。
This functions seems so powerful... just when i saw it i thought about writing a fast average of n numbers function so here it is, it is very simple... example usage included.
<?php
//Calculate the average of the numbers given
function avg(){
$sum = 0;
for($i = 0; $i < func_num_args(); $i++){
$sum += func_get_arg($i);
}
$avg = $sum / func_num_args();
return $avg;
}
echo sprintf("%.2f",avg(2,1,2,1,3,4,5,1,3,6));
?>This function may work differently from php5 to php7, in the latter it seems to reference the variable, while in php5 it returns the original argument.
I have confirmed with the versions below, but this will require further confirmation as to whether this is a 5 versus 7 issue.
function test( $test ){
$test = '123';
echo func_get_arg(0);
}
test( '321' );
//in php 5.5.9, this script will write '321'
//in php 7.0.33, this script will write '123'func_get_arg() returns a *copy* of the argument, to my knowledge there is no way to retrieve references to a variable number of arguments.
I have a module system in my game at http://lotgd.net where I'd like to be able to pass a variable number of arguments to functions in a module, and pass them by reference if the module asks for it by reference, but you can't accept optional parameters as references, nor can you retrieve the reference on a variable number of arguments. Looks like my modules will have to do with out the ability to accept parameters to their functions by reference.func_get_arg() does not appear to be allowed to be used as a function argument itself within class constructors in PHP 5.0.2 (wonk-ay!!!):
<?php
class ABC
{
function __construct()
{
foreach (func_get_args() as $name => $value)
{
echo <<<EOT
<br/>
$name : $value <br/>
<br/>
EOT;
}
}
}
class DEF extends ABC
{
function __construct()
{
parent::__construct(func_get_arg(0),
func_get_arg(1),
func_get_arg(2));
}
}
$def = new DEF(123123, "asdfasdf", "blahblahblah");
?>
The above script generates:
Fatal error: func_get_arg(): Can't be used as a function parameter in c:\Inetpub\wwwroot\phpwasrc\chapter10\xxx.php on line 23
There are, however, no problems when passing these as parameters to regular functions.I actually think that there is need for such "do absolutely everything" functions. I use them mostly as tools for rapid prototyping.
And there is a method with which you may be able to pass several strings to a function: ereg();
Another use for such functions is to create little code snippets for other people out there. They won't have to edit the function any longer if they do not use a parameter. They just don't name it when calling the function.
This results in allrounder functions that are very robust in their use.Normally you just have a little code snippet (e.g. ip-blocking snippets). Through this type of programming you have whole functions.