Question

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Is it a bug that Microsoft VS C++ compiler can Initialize a reference from a temporary object

#include <iostream>
#include <string>
using namespace std;
class test
{
public:
    string a;
public:
    test(string b){a=b;}
    friend string operator+(test);
};
string operator+(string &c,test a)
{
    c=c+a.a;
    return c;
}
void main()
{
    test d("the ");
    test e("world!");
    string s="Hello ";
     s=s+d+e;
    cout<<s<<endl;
}

the second last line s=s+d+e; after the fist overloaded operator + it returned a temporary object,and the second overloaded operator + unexpectedly worked!But the first parameter of operator+ function is a reference. why the reference of temporary object is valid here,or there is something i have missed?

P.S: It’s compiled by VC++6.0 and here is the running result.

Answer 1

Temporary objects last until the end of the full-expression in which they are created – roughly speaking, until the ; at the end of the line. References to them are valid until that point.

However, it’s not valid to bind it to a non-const reference as you do. The only reason that compiles is because your compiler is over 15 years old, and the language has been through two major changes since then. I suggest you upgrade to one of this millenium’s compilers.