/*
Filename: message_box.hpp
Date: 09.06.2007
Description: creation of message boxes
*/

#ifndef MESSAGE_BOX_HPP
#define MESSAGE_BOX_HPP

#include <windows.h>

namespace Gui {

	void mb(const TCHAR* message);

	void mb(const TCHAR* caption, const TCHAR* message);

	void mb_err(const TCHAR* message);

	void mb(HWND h, const TCHAR* message);

	void mb(HWND h, const TCHAR* caption, const TCHAR* message);

	void mb_err(HWND h, const TCHAR* message);
}

#endif

// provides implementation for 'message_box.hpp

#include "message_box.hpp"

using namespace Gui;

void mb(const TCHAR* message) {
	MessageBox(0, message, TEXT("Message"), MB_OK);
}

void mb(const TCHAR* caption, const TCHAR* message) {
	MessageBox(0, message, caption, MB_OK);
}

void mb_err(const TCHAR* message) {
	MessageBox(0, message, TEXT("Error"), MB_OK | MB_ICONERROR);
}

void mb(HWND h, const TCHAR* message) {
	MessageBox(h, message, TEXT("Message"), MB_OK);
}

void mb(HWND h, const TCHAR* caption, const TCHAR* message) {
	MessageBox(h, message, caption, MB_OK);
}

void mb_err(HWND h, const TCHAR* message) {
	MessageBox(h, message, TEXT("Error"), MB_OK | MB_ICONERROR);
}

/* test - message_box */

#include "message_box.hpp"

int WINAPI WinMain(HINSTANCE hInstance, 
				   HINSTANCE hPrevInstance, 
				   LPSTR lpCmdLine, 
				   int nShowCmd) 
{
	using namespace Gui;

	mb(TEXT("hello world"));
	mb(TEXT("information"), TEXT("unique"));
	mb_err(TEXT("wrong message"));
	return 0;
}

Endeffekt:

Error 1 error LNK2019: unresolved external symbol "void __cdecl Gui::mb_err(wchar_t const *)" (?mb_err@Gui@@YAXPB_W@Z) referenced in function _WinMain@16 unit_test.obj
Error 2 error LNK2019: unresolved external symbol "void __cdecl Gui::mb(wchar_t const *,wchar_t const *)" (?mb@Gui@@YAXPB_W0@Z) referenced in function _WinMain@16 unit_test.obj
Error 3 error LNK2019: unresolved external symbol "void __cdecl Gui::mb(wchar_t const *)" (?mb@Gui@@YAXPB_W@Z) referenced in function _WinMain@16 unit_test.obj
Error 4 fatal error LNK1120: 3 unresolved externals C:\Documents and Settings\Zdravko\My Documents\Visual Studio 2005\Projects\gui_fundaments\Debug\gui_fundaments.exe 1

Warum?

Ist die CPP Datei wirklich in das Projekt eingefügt worden?
Sind alle CPP Dateien garantiert mit den selben Compiler Optionen kompiliert?

Ja!

#include "message_box.hpp" 

namespace Gui
{
void mb(const TCHAR* message) { 
	MessageBox(0, message, TEXT("Message"), MB_OK); 
} 
[snip]
}