函数

isset

检测变量是否已设置并且非 NULL

parse_url

解析 URL，返回其组成部分

$url = 'http://username:password@hostname/path?arg=value#anchor';
print_r(parse_url($url));

输出结果：
Array
(
    [scheme] => http
    [host] => hostname
    [user] => username
    [pass] => password
    [path] => /path
    [query] => arg=value
    [fragment] => anchor
)