Compiling Error with C++ and namespace

Question

Here's the whole code getting the errors:

Engine.h

#ifndef ENGINE_H
#define ENGINE_H

#include "DXManager.h"

namespace XEngine
{
    class Engine
    {
    };
}

#endif

DXManager.h

#ifndef DX_MANAGER_H
#define DX_MANAGER_H



namespace XEngine
{
    class Engine; // forward declaration

    class DXManager
    {
    public:
        void run(Engine *engine);
    };
}

#endif

DXManager.cpp

#include <iostream>

#include "Engine.h"
#include "DXManager.h"

using namespace XEngine;

void DXManager::run(Engine *engine)
{
    std::cout<<"DXManager::run"<<std::endl;
}

With these 30 lines of code, I'm getting 20 errors like:

'XEngine' : a namespace with this name does not exist
'XEngine' : a symbol with this name already exists and therefore this name cannot be used as a namespace name
syntax error : identifier 'Engine'

Clearly, I'm missing something important here. What am I doing wrong?

note: I am aware that circular dependency is a bad thing, but in my particular case I believe that it is relevant.

Your code compiles on MSVC 10 after the edit. It must be another error in another piece of code. — Khaled Nassar
– Khaled Nassar, Commented Apr 4, 2011 at 2:24
Indeed. I guess I didn't do the appropriate modification on my real code. Thanks a lot for your help! — Jesse Emond
– Jesse Emond, Commented Apr 4, 2011 at 2:28
Are the errors coming from dxmanager.cpp or from another compilation unit that includes engine.h and/or dxmanager.h? — greatwolf
– greatwolf, Commented Apr 4, 2011 at 2:46

Serge Dundich · Accepted Answer · 2011-04-04 02:28:20Z

3

In DXManager.cpp you are not just using some names from namespace XEngine. You define the function in that namespace.

So must be:

DXManager.cpp

#include <iostream>

#include "Engine.h"
#include "DXManager.h"

namespace XEngine {

void DXManager::run(Engine *engine)
{
    std::cout<<"DXManager::run"<<std::endl;
}

}

AFAIK some of the compilers (like MSVC) process using variant too. But it is not correct because your syntax tries to define function ::DXManager::run - not ::XEngine::DXManager::run you intend to define.

answered Apr 4, 2011 at 2:28

Serge Dundich

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1 Comment

Jesse Emond Over a year ago

I'm taking a mental note of this. Thanks for the information.

Khaled Nassar · Accepted Answer · 2011-04-04 02:15:08Z

2

In the forward-declaration of class Engine the namespace XEngine doesn't exist at this point.

A workaround would be moving the declaration inside the namespace block.

answered Apr 4, 2011 at 2:15

Khaled Nassar

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1 Comment

Jesse Emond Over a year ago

Thanks for pointing it out. Still 10 errors left though.. =/ The same type of errors.

Javier · Accepted Answer · 2011-04-04 02:18:03Z

1

When Engine.h includes DXManager.h, the latter defines a class XEngine::Engine without declaring the namespace first.

answered Apr 4, 2011 at 2:18

Javier

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1 Comment

Jesse Emond Over a year ago

I moved the forward declaration within the namespace, but I'm still getting the errors though.

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