I'm doing my first project with multiple files and I'm having trouble for some reason. I used the example for multiple source files lazyfoo.net has and while it did help ease my confusion somewhat, I am still getting errors:

1>Pong.obj : error LNK2005: "struct SDL_Surface * sScreen" (?sScreen@@3PAUSDL_Surface@@A) already defined in Functions.obj
1>Pong.obj : error LNK2005: "int const SCREEN_WIDTH" (?SCREEN_WIDTH@@3HB) already defined in Functions.obj
1>Pong.obj : error LNK2005: "int const SCREEN_HEIGHT" (?SCREEN_HEIGHT@@3HB) already defined in Functions.obj
1>Pong.obj : error LNK2005: "int const SCREEN_BPP" (?SCREEN_BPP@@3HB) already defined in Functions.obj
1>Pong.obj : error LNK2005: "struct SDL_Surface * pongSprites" (?pongSprites@@3PAUSDL_Surface@@A) already defined in Functions.obj
1>C:\Users\Brandon\Documents\Visual Studio 2010\Projects\Pong\Release\Pong.exe : fatal error LNK1169: one or more multiply defined symbols found

Pong.cpp


#include "Functions.h"
#include "Globals.h"
#pragma region Main
int main(int argc, char* argv[])
{

#pragma region Setup
//Quit flag
bool quit = false;
#pragma endregion Setup
#pragma region Game Logic
//While the user hasn't quit
while( quit == false )
{
//While there's events to handle
while( SDL_PollEvent( &event ))
{

//If the user has Xed out the window
if( event.type == SDL_QUIT )
{
//Quit the program
quit = true;
}
}

#pragma endregion Game Logic
#pragma region Rendering
SDL_FillRect(sScreen,NULL, 0x000000);
//Update Screen
SDL_Flip( sScreen );
#pragma endregion Rendering
}
return 0;
}
#pragma endregion Main


Globals.h


#ifndef GLOBALS_H
#define GLOBALS_H
#include "SDL.h"
#include "SDL_image.h"
extern SDL_Surface* sScreen = NULL;
extern const int SCREEN_HEIGHT = 700;
extern const int SCREEN_WIDTH = 600;
extern const int SCREEN_BPP = 32;
extern SDL_Event event;
extern SDL_Surface* pongSprites = NULL;
#endif


Functions.h


#ifndef FUNCTIONS_H
#define FUNCTIONS_H
#include "SDL.h"
#include "SDL_image.h"
#include <string>

bool init();
SDL_Surface *load_image( std::string filename );
void apply_surface( int x, int y, SDL_Surface* source, SDL_Surface* destination, SDL_Rect* block );
bool load_files();

#endif


Functions.cpp


#include "Functions.h"
#include "SDL.h"
#include "SDL_image.h"
#include "Globals.h"
#include <string>

#pragma region Init

bool init()
{
//Initialize all SDL subsystems
if( SDL_Init( SDL_INIT_EVERYTHING ) == -1 )
{
return false;
}
//Set up the screen
sScreen = SDL_SetVideoMode( SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_BPP, SDL_SWSURFACE );
//If there was an error in setting up the screen
if( sScreen == NULL )
{
return false;
}
//Set the window caption
SDL_WM_SetCaption( "Pong", NULL );
//If everything initialized fine
return true;
}

#pragma endregion Init
#pragma region Load_image
//-------------------------------------------------
SDL_Surface *load_image( std::string filename )
{
//The image that's loaded
SDL_Surface* loadedImage = NULL;
//The optimized surface that will be used
SDL_Surface* optimizedImage = NULL;
//Load the image
loadedImage = IMG_Load( filename.c_str() );
//If the image loaded
if( loadedImage != NULL )
{
//Create an optimized surface
optimizedImage = SDL_DisplayFormat( loadedImage );
//Free the old surface
SDL_FreeSurface( loadedImage );
//If the surface was optimized
if( optimizedImage != NULL )
{
//Color key surface
SDL_SetColorKey( optimizedImage, SDL_SRCCOLORKEY, SDL_MapRGB( optimizedImage->format, 0, 0xFF, 0xFF ) );
}
}
//Return the optimized surface
return optimizedImage;
}
//-------------------------------------------------
#pragma endregion Load_image
#pragma region Load_Files
bool load_files()
{
pongSprites = load_image("pong.png");

if(pongSprites != NULL)
return true;
else
return false;
}
#pragma endregion Load_Files
#pragma region Apply_Surface
void apply_surface( int x, int y, SDL_Surface* source, SDL_Surface* destination, SDL_Rect* block )
{
//Holds offsets
SDL_Rect offset;
//Get offsets
offset.x = x;
offset.y = y;
//Blit
SDL_BlitSurface( source, block, destination, &offset );
}
#pragma endregion Apply_Surface


Thank you for any help in getting over this next obstacle, I do appreciate it.

Don't do the assignment of the extern variables in the header file, that turns the extern declaration into a definition and your linker is complaining about multiple definitions. Only declare them with extern in the header, and define them without the extern in one source file.

header:

extern SDL_Surface* sScreen;

source:

SDL_Surface* sScreen = NULL;


You don't have to do the extern declaration for primitive const variables such as your integer, though. They have static linkage by default, so you can leave them in the header file but remove the extern from them.

extern SDL_Surface* sScreen = NULL;
extern const int SCREEN_HEIGHT = 700;
extern const int SCREEN_WIDTH = 600;
extern const int SCREEN_BPP = 32;
extern SDL_Event event;
extern SDL_Surface* pongSprites = NULL;[/quote]

For sScreen and pngSprints (the non-const of the bunch), don't initialize them here. Instead, initialize them wherever you define them (a single .cpp file).

For SCREEN_HEIGHT, SCREEN_WIDTH and SCREEN_BPP (the const of the bunch), remove the `extern' and everything will work fine.

`event' should probably not be a global variable at all: It should be a local variable in `main', and it should be passed around only to functions that might need it.