Adding namespace functions in header files [closed] - c++

Question

Closed. This question is not reproducible or was caused by typos. It is not currently accepting answers.
This question was caused by a typo or a problem that can no longer be reproduced. While similar questions may be on-topic here, this one was resolved in a way less likely to help future readers.
Closed 4 years ago.
Improve this question
I'm trying to use header files to transfer functions in a namespace on a separate file to another file, and it's returning the error
"Add" is not a member of "simple".
I simply want to know if it's possible to use forward function declarations rather than declaring the function every time in the header, which supposedly would keep copying the code for every .cpp that includes it.
Here's the basic outline for 1.cpp, 2.cpp and 3.h.
1.cpp
#include "stdafx.h"
// Check this header file for function declarations.
#include "3.h"
int main()
{
//Example of a single namespace.
std::cout << simple::add(3, 4);
return 0;
}
2.cpp
#include "stdafx.h"
namespace simple {
int simple::add(int x, int y) {
return x + y;
}
}
3.h
#ifndef NAMESPACES
#define NAMESPACES
namespace simple {
int simple::add(int, int);
}
#endif
Much appreciation to anyone who answers, and apologies if this has been asked before.

Answer 1

Figured out the issue, for any future viewers of this thread.
You don't use the prepending "simple::" on header declarations, or in the function itself, as I did.
Corrected code:
3.h
#ifndef NAMESPACES
#define NAMESPACES
//Header guards are important!
namespace simple {
int add(int, int);
}
#endif
2.cpp
#include "stdafx.h"
#include "3.h"
int simple::add(int x, int y) {
return x + y;
}
No changes are required to 1.cpp.