Re: Throwing a reference to a temporary object

From:

anon <anon@no.no>

Newsgroups:

comp.lang.c++

Date:

Wed, 17 Oct 2007 11:53:18 +0200

Message-ID:

<ff4m2g$qgb$1@el-srv04-CHE.srvnet.eastlink.de>

Dario Menendez wrote:

Is it possible to throw a reference to a temporary object?
Will the temporary object be copied one or more times?

See following example:

struct my_exception
{
    my_exception(int i) : i_(i) {}
    my_exception& ref() {return *this;}
    int i_;
}

void f_throws()
{
    throw my_exception(3).ref();
}

int main()
{
    try {
        f_throws();
    }
    catch(my_exception& e) { return e.i_; }
    return 0;
}

I modified your example bit:

#include <iostream>

struct my_exception
{
     my_exception(int i) : i_(i)
     { std::cout<<"constr i="<<i<<std::endl;}
     my_exception(const my_exception &c)
     { this->i_ = c.i_;std::cout<<"cc"<<std::endl;}
     const my_exception& ref()
     { std::cout<<"in ref()"<<std::endl; return *this;}
     int i_;
};

void f_throws()
{
     std::cout<<"throwing"<<std::endl;
     throw my_exception(3).ref();
     //throw my_exception(3);
}

int main()
{
     try
     {
         f_throws();
     }
     catch( const my_exception &e )
     {
         return e.i_;
     }
     return 0;
}

It gave me the answer to your question: one copy.