PHP判断(函数/类/方法/属性)是否存在

if(function_exists('curl_init')){

    curl_init();

}else{

    echo 'not function curl_init';

}

if(class_exists('MySQL')){

    $myclass=new MySQL();

}

$directory=new Directory;

if(!method_exists($directory,'read')){

    echo '未定义read方法！';

}

$directory=new Directory;

if(!property_exists($directory,'li')){

    echo '未定义li属性！';

}