C++ Unresolved Externals because of header

Question

I just started with C++ for some OpenGL applications and wanted to pack some monster functions into a util class so that my code remains clean. This is what I did:

1. awesomeClass.h :

   #pragma once    
   class AwesomeClass    
   {    
   public:    
       static void do_something_awesome();    
   };    
   

2. awesomeClass.cpp :

   #include "awesomeClass.h"    
   void do_something_awesome(){    
    //...    
   }    
   

3. main.cpp :

   #include "awesomeClass.h"    
   int main(int argc, char** argv)    
   {    
       AwesomeClass::versuchen();    
       return 0;    
   }
   

Output:

Error   3   error LNK1120: 1 unresolved externals   \Visual Studio 2013\Projects\TestEnvironmment\Debug\TestEnvironmment.exe    TestEnvironmment

Error   2   error LNK2019: unresolved external symbol "public: static void __cdecl AwesomeClass::do_something_awesome(void)" (?do_something_awesome@AwesomeClass@@SAXXZ) referenced in function _SDL_main   \Visual Studio 2013\Projects\TestEnvironmment\TestEnvironmment\main.obj TestEnvironmment

What is wrong with that code? I mean it works when I paste everything in one file.

Answer 1

You should write

void AwesomeClass::do_something_awesome(){... } 

Instead of

void do_something_awesome(){... } 

Otherwise the function you implement does not belong to the class.

Answer 2

You should write this if you want write do_something_awesome in separate cpp file.

void AwesomeClass::do_something_awesome(){    
 //...    
} 

Or you can use:

    #pragma once    
    class AwesomeClass    
    {    
    public:    
        static void do_something_awesome(){
        //code here
        }  

    };