class Ctx{
public:
    void foo1(){
        depth++;
        foo2();
        depth--;
    }

    void foo2(){
        if ( something ){
            foo1();
        }else if ( something2 ){
            try{
                foo_try_this_one();
            }catch(Exception&){
                foo_backup(); // here the depth may become invalid
            }
        }else{
            ...
        }
    }

    void foo_try_this_one();
    void foo_backup();

    int depth;
};