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From: "zeratul976 at hotmail dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/52145] New: [C++11] zero-valued integer constant expression should prefer conversion to pointer
Date: Tue, 07 Feb 2012 01:00:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=52145

             Bug #: 52145
           Summary: [C++11] zero-valued integer constant expression should
                    prefer conversion to pointer
    Classification: Unclassified
           Product: gcc
           Version: 4.7.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: zeratul976@hotmail.com


In the following example:

#include <iostream>
using std::cerr;

struct S { int n; };
struct X { X(int) {} };
void f(void*)
{
    cerr << "Pointer!\n";
}
void f(X)
{
    cerr << "X!\n";
}
int main()
{
    f(S().n);
}

With GCC 4.7.0-20120128 with the --std=c++11 flag, the output is "X!". The
correct output would be "Pointer!".

The reason is that S's implicit default constructor is constexpr, so it
value-initializes n. Therefore S().n is a zero-valued integer constant
expression, whose conversion to a pointer is preferred over the user-defined
conversion to X.

(This example was taken from Chandler Carruth's talk at the GoingNative 2012
conference.)