How to prevent macro redefinition

Question

After working some time on my project, this warning begins to appear:

2>Game.cpp
2>c:\\program files\\microsoft sdks\\windows\\v6.0a\\include\\windef.h         


        

Answer 1

Microsoft doesn't generally design headers to be free-standing. Most of the Windows-oriented headers require that you have first included <windows.h>. Except for the dependency on that Mother Of All Headers, usually there are no specific header dependencies so by including <windows.h> first you shouldn't have any problem.

Answer 2

This may be caused by Visual Studio pre-compiling headers for you. Be sure that all standard and microsoft headers are included before yours. Don't include microsoft headers in any of your .h files (it looks like you have windef.h and wingdi.h inlcuded in your glfw.h). Be sure that all your headers are side-effect free. The problem should then go away. Figuring out exactly what is causing it is generally very hard.

Answer 3

Unfortunately or fortunately, no. There is no such tool that automates it. You have to go read the code in those header files, figure out what is going on and take appropriate actions.

The most you can do is

1. Check if macro is defined using ifdef or if defined(...) or if !defined(...) preprocessor constructs.
2. Undefine macro using undef.

Only ANSI C considers macro redefinition an error.

Answer 4

The error message itself is telling you the incorrect order. It says that windef.h and wingdi.h are redefining symbols that were defined in glfw.h.

Put glfw.h after the Windows include files.

Answer 5

The problem is in the file Game.cpp. Try to include windows.h before glfw.h. There is a guard in glfw.h which will prevent that warning:

#ifndef APIENTRY
 #ifdef _WIN32
  #define APIENTRY __stdcall
 #else
  #define APIENTRY
 #endif
 #define GL_APIENTRY_DEFINED
#endif // APIENTRY