Re: Valid C++, or not?

From:

int19h@gmail.com

Newsgroups:

comp.lang.c++.moderated

Date:

Fri, 28 Sep 2007 13:29:06 CST

Message-ID:

<1191000555.064839.251640@50g2000hsm.googlegroups.com>

On 28 Sep, 21:00, loose AT astron DOT nl <lo...@astron.nl> wrote:

   Is this valid C++ (and hence a compiler bug), or is it not.?

BTW: GCC 4.2.1 will happily compile the code, when I make the friend
ostream& operator<<() global.

#include <iostream>
#include <map>
#include <string>
#include <vector>

using namespace std;

struct KeyValue
{
   KeyValue() {}
   KeyValue(bool) {}
   KeyValue(const vector<bool>&) {}
   vector<bool> getVecBool() const { return vector<bool>(); }
   friend ostream& operator<<(ostream& os, const KeyValue&) { return
os; }

};

int main()
{
   map<string, KeyValue> par;
   par["b1"] = true;
   cout << par["b1"].getVecBool() << endl;}

No, this is not valid C++. The reason why it does not work is that
your operator<< overload is only considered when one of the arguments
is a KeyValue, according to the usual rule for inline friend
definitions. In your case, the two arguments are std::ostream and
std::vector<bool>; therefore, the overloaded operator<< does not even
appear in the overload set, and the conversion is not considered
either. If you want this to work, you have to define operator<<
outside KeyValue.

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