Article ID: 168078
Article Last Modified on 10/24/2003
APPLIES TO
- Microsoft Visual C++ 5.0 Enterprise Edition
- Microsoft Visual C++ 5.0 Professional Edition
This article was previously published under Q168078
SYMPTOMS
When you attempt to instantiate an STL component for a class, a C2784 error occurs, complaining that a relational operator (such as operator!= or operator>) is not defined. This in spite of including "using namespace std::rel_ops;", and defining operator< and operator== for the class.
CAUSE
The problem is caused by the nested namespace std::rel_ops. The compiler is unable to do a proper name lookup for the generic relational operators '!=', '<=', '>', '>=', which are defined in the namespace std::rel_ops and are referenced by several STL components.
RESOLUTION
The easiest workaround is to add a using declaration for the specific operator the compiler is complaining about. See the sections compiled conditionally upon WORKAROUND in the sample code below.
STATUS
Microsoft has confirmed that this is a problem in the Microsoft products that are listed at the beginning of this article. This problem was corrected in Microsoft Visual C++ version 6.0.
MORE INFORMATION
The following sample demonstrates the problem.
Sample Code
/*
Compile options: /GX
*/
#include <list>
using namespace std ;
using namespace std::rel_ops ;
#ifdef WORKAROUND // define WORKAROUND to get around the error
using std::rel_ops::operator!=;
using std::rel_ops::operator>;
#endif
class X {
int N;
public:
X(int n) : N(n) {}
bool operator==(const X& b) const
{ return N == b.N; }
bool operator<(const X& b) const
{ return N < b.N; }
};
list <X> xList;
int main()
{
return 0;
}
Keywords: kbbug kbfix kbvc600fix KB168078
