<?php
try{
    //错误或异常
}catch (Exception $ex){
    //处理异常
    //抛出异常
}

<?php
function my_exception($e){
    echo "我是顶级异常处理";
}
set_exception_handler("my_exception");
try{
    addUser('aaa');
    echo '操作成功！';
}catch (Exception $e){
    throw $e;
}


function addUser($username){
    if($username == 'a'){
        return true;
    }else{
        throw new Exception('添加失败！');
    }
}

<?php
class MyException1 extends Exception{

}

class MyException2 extends Exception{

}

function A(){
    throw new MyException1("a");
}
function B(){
    throw new MyException2("b");
}

try{
    A();
    B();
}catch (MyException1 $e1){
    echo $e1->getMessage();
}catch (MyException2 $e2){
    echo $e2->getMessage();
}