Re: Why this does not compile on g++ but works in Visual C++ 2008

From:

Paul Bibbings <paul.bibbings@gmail.com>

Newsgroups:

comp.lang.c++

Date:

Sat, 10 Jul 2010 12:50:20 +0100

Message-ID:

<87zkxztv2b.fsf@gmail.com>

Sam <sam@email-scan.com> writes:

Jag writes:

virtex<T>* add_a_virtex(const virtex<T>& v1) {
     //set<virtex<T> > _vertices ;
     pair<set<virtex<T> >::iterator,bool> itt = _vertices.insert(v1) ;
     /* code removed below */
}
on g++ I get this error.

sgraph.h: In member function `virtex<T>* sgraph<T>::add_a_virtex(const
virtex<T>&)':
sgraph.h:95: error: type/value mismatch at argument 1 in template
parameter list for `template<class _T1, class _T2> struct std::pair'
sgraph.h:95: error: expected a type, got `
std::set<virtex<T>,std::less<virtex<T> >,std::allocator<virtex<T> >

::iterator'

sgraph.h:95: error: invalid type in declaration before '=' token

Can some kind soul help me to fix the issue using g++.

There's probably a problem somewhere in either the definition of your
virtex template class, or your _vertices object. However, because you
neglected to post your class definitions, no further help is possible.

The only thing that I can tell you is that the following complete
example which, as far as I can tell using my best guess, is
structurally equivalent with your use case, compiles just fine with
g++ 4.4.4:

#include <set>

template<typename T> class virtex {

public:
    bool operator<(const virtex<T> &) const;
};

class T {

};

std::set< virtex<T> > _vertices;

void add_a_virtex(const virtex<T> &v1)
{
    std::pair<std::set<virtex<T> >::iterator, bool>
        itt=_vertices.insert(v1);
}

This is a complete example that compiles, but it does not contain the
crucial element of the OP's code that leads to the error message. As
you can see from the error output, add_a_virtex(const virtex<T>&) is a
member function of a parameterized type:

   template<typename T>
   struct sgraph {
   public:
      vertex<T> * add_a_vertex(const vertex<T>&);
      // ...
   };

You have add_a_virtex(const vertex<T>&) as a non-parameterized free
function and have had to arbitrarily define a class T in order to fit
the OP's problem to your example (which might have been a clue :). The
interpretation from both Jonathan and Alf is the correct one.

Regards

Paul Bibbings