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already defined in main.obj

Started by Mozly Apr 18, 2011 at 1:57 AM 12 replies 5.7k views

Original Post

Apr 18, 2011 at 1:57 AM

I am getting this error when I try to compile:

1>Particle.obj : error LNK2005: "struct SDL_Surface * red" (?red@@3PAUSDL_Surface@@A) already defined in main.obj
1>Particle.obj : error LNK2005: "struct SDL_Surface * blue" (?blue@@3PAUSDL_Surface@@A) already defined in main.obj
1>Particle.obj : error LNK2005: "struct SDL_Surface * green" (?green@@3PAUSDL_Surface@@A) already defined in main.obj

Source file:

#include "Particle.h"
 
 Particle::Particle(int X, int Y)
 {
 x = X + 5 + (rand()%25);
 y = Y + 5 + (rand()%25);
 
 frame = rand() % 5;
 
 switch(rand()%3)
 {
 case 0:
 type = red;
 break;
 case 1:
 type = green;
 break;
 case 2:
 type = blue;
 break;
 }
 }

Header File:

#pragma once
 #include <SDL.h>
 
 SDL_Surface *red;
 SDL_Surface *green;
 SDL_Surface *blue;
 SDL_Surface *shimmer;
 
 #ifndef PARTICLE
 #define PARTICLE
 
 
 class Particle
 {
 protected:
 //offsets
 int x,y; 
 
 // current frame of animation
 int frame;
 
 //type of particle
 SDL_Surface* type;
 
 public:
 Particle(int X, int Y);
 ~Particle(void);
 void show();
 bool is_dead();
 };
 
 #endif

I know its because I include particles.h in this source file and in my main source file (I figured this out because I researched this type of error before positing).
I Really need red, green and blue to be global variables. what can I do to get rid of this error

Hodgman

Apr 18, 2011 at 2:09 AM

In one CPP file:

SDL_Surface *red = 0;//make a global variable named 'red'
 SDL_Surface *green = 0;
 SDL_Surface *blue = 0;
 SDL_Surface *shimmer = 0;

In a header file (which means copied into multiple CPP files):

extern SDL_Surface *red;//declare that there is a global variable named 'red' *somewhere*
 extern SDL_Surface *green;
 extern SDL_Surface *blue;
 extern SDL_Surface *shimmer;

smart_idiot

Apr 18, 2011 at 2:09 AM

Put 'extern SDL_Surface *red, *green, *blue, *shimmer;' in the header file, and put 'SDL_Surface *red, *green, *blue, *shimmer;' inside the source file.

Mozly

Apr 18, 2011 at 2:21 AM

In one CPP file:SDL_Surface *red = 0;//make a global variable named 'red' SDL_Surface *green = 0; SDL_Surface *blue = 0; SDL_Surface *shimmer = 0;

So I copied that into my source file so it looks like this now

#include "Particle.h"
 
 SDL_Surface *red = 0;//make a global variable named 'red'
 SDL_Surface *green = 0;
 SDL_Surface *blue = 0;
 SDL_Surface *shimmer = 0;
 
 Particle::Particle(int X, int Y)
 {
 x = X + 5 + (rand()%25);
 y = Y + 5 + (rand()%25);
 
 frame = rand() % 5;
 
 switch(rand()%3)
 {
 case 0:
 type = red;
 break;
 case 1:
 type = green;
 break;
 case 2:
 type = blue;
 break;
 }
 }

but now I get this error
1>c:\users\mishu\desktop\documents\visual studio 2010\projects\sdl tut 27 particles engine\sdl tut 27 particles engine\particle.cpp(3): error C2086: 'SDL_Surface *red' : redefinition
1> c:\users\mishu\desktop\documents\visual studio 2010\projects\sdl tut 27 particles engine\sdl tut 27 particles engine\particle.h(8) : see declaration of 'red'

Doesn't that mean that I'm declaring these variable twice?

Mozly

Apr 18, 2011 at 2:27 AM

Put 'extern SDL_Surface *red, *green, *blue, *shimmer;' in the header file, and put 'SDL_Surface *red, *green, *blue, *shimmer;' inside the source file.

Now that I added extern it works. But I dont get why?

smart_idiot

Apr 18, 2011 at 2:33 AM

[quote name='smart_idiot' timestamp='1303092583' post='4799705']
Put 'extern SDL_Surface *red, *green, *blue, *shimmer;' in the header file, and put 'SDL_Surface *red, *green, *blue, *shimmer;' inside the source file.

Now that I added extern it works. But I dont get why?
[/quote]

Extern is compiler speak for 'Please just take it on faith that this variable exists and that the linker is going to tell you where at some as of yet unknown time and place.'

Mozly

Apr 18, 2011 at 2:37 AM

one more thing,
in my header I declare some constant integers which I want as global variables but keep getting the old error that it is already defined in the main obj.

Here that header:

#include <SDL.h>
 #include <SDL_image.h>
 #include <string>
 
 
 #ifndef GLOBALFNS
 #define GLOBALFNS
 
 extern "C++"{
 
 //declare some poiters
 SDL_Surface *dot;
 extern SDL_Surface *screen;
 
 
 
 //The dimensions of the dot
 const int DOT_WIDTH = 20;
 const int DOT_HEIGHT = 20;
 
 SDL_Event event;
 
 int ScreenW = 640;
 int ScreenH = 480;
 
 //total paticles
 const int TOTAL_PARTICLES = 20;
 
 //SDL supporting functions start
 SDL_Surface* loadimg(std::string filename);
 
 void applysurface(int x, int y, SDL_Surface* src, SDL_Surface* dst, SDL_Rect* clop);
 }
 
 #endif

Hodgman

Apr 18, 2011 at 2:41 AM

use 'const static' instead of 'const'.

In this usage, static means "keep it local to this file, don't bother the linker with this variable"

Your ScreenW/ScreenH will cause trouble though -- they should be in a CPP file, and then have 'extern' versions of them in the header.

Mozly

Apr 18, 2011 at 2:53 AM

still one little thing,

How do you globally define a union type like SDL_Event event in a header file? Because I keep getting this error

1>main.obj : error LNK2001: unresolved external symbol "union SDL_Event event" (?event@@3TSDL_Event@@A)

even though I declared it as an external variable

smart_idiot

Apr 18, 2011 at 3:00 AM

still one little thing,

How do you globally define a union type like SDL_Event event in a header file? Because I keep getting this error

1>main.obj : error LNK2001: unresolved external symbol "union SDL_Event event" (?event@@3TSDL_Event@@A)

even though I declared it as an external variable

Hello? Hello? Anybody home? Huh? Think, McFly. Think! I gotta have time to get 'em retyped. Do you realize what would happen if I hand in my reports in your handwriting? I'll get fired. You wouldn't want that to happen, would ya? Would ya?

The union isn't special, you stick a non-extern copy of it in a source file like you did with everything else... although I'm really doubtful there's a good reason your event object needs to be seen globally.

Mozly

Apr 18, 2011 at 3:09 AM

.. although I'm really doubtful there's a good reason your event object needs to be seen globally.

The event handling happens in my classes which I define in other source files

But thanks I finally have this thing running

smart_idiot

Apr 18, 2011 at 3:11 AM

I fear the dependency graph for your program is going to look like a bowl of tangled spaghetti.

Mozly

Apr 18, 2011 at 3:22 AM

Its a relatively small program im using to learn how to make my future projects modular coz I'm tired of programs with over 9000 lines of code =).

Mozly

Apr 20, 2011 at 12:07 AM

Ok, So I wrote about the error on my Blog. If you read it let me know if I made any mistakes and if I can add anything.

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