Question

I have this problem:

template<typename T> class Bubu
{
...
   int (*comparer)(const T t1, const T t2);
...
public:
   Bubu(int (*_comparer)(const T t1, const T t2))
   {
      comparer = _comparer;
   }
};

And in another file:

Bubu<char*> asd(strcmp);

Error:

error C2664: 'Bubu<T>::Bubu(int (__cdecl *)(const T,const T))' : 
             cannot convert parameter 1 from 'int (__cdecl *)(const char *,
             const char *)' to 'int (__cdecl *)(const T,const T)'

I don’t understand why. Shouldn’t the compiler see a “char*” instead of “T” there?

EDIT: the Ideone.com-ready code:

int asdf(const char* a, const char* b)
{       return 0; }

template class Bubu
{
   int (*comparer)(const T t1, const T t2);
public:
   Bubu(int (*_comparer)(const T t1, const T t2))
   {
      comparer = _comparer;
   }
};

int main(int argc, char* argv[])
{
Bubu asd(asdf);
}

Answer 1

When T is char*, const T is char* const which isn’t the same thing as const char *. You need:

 Bubu<const char*> asd(strcmp);

Top level const is ignored for function signatures so

int (*)( const char* const, const char* const );

is the same type as

int (*)( const char*, const char* );

so you’re OK on the extra top level const although it doesn’t gain you anything over the simpler int (*comparer)(T t1, T t2);.