One or more multiply defined symbols found

Question

DebugUtil.h

#ifndef DEBUG_UTIL_H #define DEBUG_UTIL_H  #include <windows.h>  int DebugMessage(const char* message) {     const int MAX_CHARS = 1023;     static char s_buffer[MAX_CHARS+1];      return 0; }  #endif 

When I try to run this I get this error:

Terrain.obj : error LNK2005: "int __cdecl DebugMessage(char const *)" (?DebugMessage@@YAHPBD@Z) already defined in Loodus.obj

Renderer.obj : error LNK2005: "int __cdecl DebugMessage(char const *)" (?DebugMessage@@YAHPBD@Z) already defined in Loodus.obj

test.obj : error LNK2005: "int __cdecl DebugMessage(char const *)" (?DebugMessage@@YAHPBD@Z) already defined in Loodus.obj

C:\Users\Tiago\Desktop\Loodus Engine\Debug\Loodus Engine.exe : fatal error LNK1169: one or more multiply defined symbols found

But why does this happen? I have #ifndef #define and #endif in the header so multiple definitions shouldn't happen

Answer 1

Put the definition (body) in a cpp file and leave only the declaration in a h file. Include guards operate only within one translation unit (aka source file), not across all your program.

The One Definition Rule of the C++ standard states that there shall appear exactly one definition of each non-inline function that is used in the program. So, another alternative would be to make your function inline.