Re: Simple question: extending lifetime of temporaries with a reference

I've heard of "extending the lifetime of a temporary
by binding it to a reference", but am not entirely
sure of when that applies.

My impression is that if you do, say:

     // sample 1
     std::string str1( "String 1\n");
     std::string str2( "string 2\n");
     std::string &str_sum = str1 + str2;
     std::cout << str_sum << str::endl;

then the temporary object "str1 + str2" won't be destroyed
until str_sum goes out of scope.

On the other hand, I'm fairly convinced that

     // sample 2
     std::string &f() { std::string temp( "temp value"); return temp; }
     void g() {
         std::string &ret_val = f();
         std::cout << ret_val << std::endl;
     }

won't work.

1. Is this correct, or am I just terminally bewildered?