func_num_args, func_get_arg, func_get-args 的区别与用法

<?php
header("Content-Type: text/html; charset=UTF-8");

function foo()
{
    $numargs = func_num_args();
    echo "参数个数为： $numargs\n";
}

foo(1, 2, 3);   
?>

<?php
header("Content-Type: text/html; charset=UTF-8");

function foo()
{
    $numargs = func_num_args();
    echo "参数个数为： $numargs<br />\n";
    if ($numargs >= 2) {
        echo "第2个参数是：" . func_get_arg(1) . "<br />\n";
    }
    $arg_list = func_get_args();
    var_dump($arg_list);
}

foo(1, 2, 3);
?>

<?php
header("Content-Type: text/html; charset=UTF-8");

function foo()
{
     $numargs = func_num_args();
     echo "参数个数是： $numargs<br />\n";
     if ($numargs >= 2) {
         echo "第2个参数是：" . func_get_arg(1) . "<br />\n";
     }
}

foo (1, 2, 3);
?>