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Ralph Zhang · Guest

Hi,

I am reading Modern C++ Design and it mentions typetraits of pointer to
member function, so I write the following program to test that:

-------------------------------------------------------------------------------
#include <iostream>
template <typename T>
class TypeTraits
{
private:
template <class U> struct PtoMTraits
{
enum {result = false};
};

template <class U, class V> struct PtoMTraits<U V::*>
{
enum {result = true};
};

public:
static const bool isPtoM = PtoMTraits<T>::result;
};

struct Empty
{
int MemFun(int){return 0;}
};

int main()
{
typedef int(Empty::*PtoMType)(int);
PtoMType pTomf = &Empty::MemFun;

bool isPtoM = TypeTraits<PtoMType>::isPtoM;
std::cout << "is a pointer to member function: " << isPtoM <<
std::endl;
}
-------------------------------------------------------------------------------
It compiles both on VC7.1 and g++ 3.3.3(cygwin), but the VC7.1
executable gives:
is a pointer to member function: 1
while the g++ executable gives
is a pointer to member function: 0

And on BCB5.5 it doesn't compile at all.

What's wrong with them? As 1 is my intentioned result, is that a bug of
g++?

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Sharad Kala · Guest

"Ralph Zhang" <ralph623 (AT) 126 (DOT) com> wrote in message

L.Suresh · Guest

This template specialization expectes a pointer to a member, not a
member function.

template <class U, class V> struct PtoMTraits<U V::*>
{
enum {result = true};
};

This will work...

struct Empty
{
int mem;
};

int main() {
typedef int (Empty::*PtoMType);
.....
}

--lsu

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