Returns the argument which is at the arg_num'th offset into a user-defined function's argument list. Function arguments are counted starting from zero. func_get_arg() will generate a warning if called from outside of a function definition. This function cannot be used directly as a function parameter. Instead, its result may be assigned to a variable, which can then be passed to the function.
If arg_num is greater than the number of
arguments actually passed, a warning will be generated and
func_get_arg() will return FALSE.
因为本函数依赖于当前域来决定参数细节，因此不能用作函数参数。如果必须要传递这个值，将结果赋给一个变量，然后传递该变量。
<?php
function foo()
{
$numargs = func_num_args();
echo "Number of arguments: $numargs<br />\n";
if ($numargs >= 2) {
echo "Second argument is: " . func_get_arg(1) . "<br />\n";
}
}
foo (1, 2, 3);
?>func_get_arg() may be used in conjunction with func_num_args() and func_get_args() to allow user-defined functions to accept variable-length argument lists.