Header and Source file problems in Code::Blocks - c

Question

I am programming a game in C using Code::Blocks. I am using the most recent version of C and of Code::Blocks. I am still learning the language.
All of my past programs have been contained in one huge source file, so I decided to branch out and try putting my code in multiple files. I know that the proper way to do it is to have source files containing code definitions and such and a header file containing prototypes for other source files to use. This has worked out horribly for me and I either can't get the files to work together properly or it simply doesn't work period.
I have a single function in a source file called process.c and a function prototype in a file called process.h. I also have a main.h and a main.c containing all the rest of the code. The main issue is that I have a typedef struct Game in my main.h file and I can't get the 'Game' struct type I created to work in my process.c. Every function in my game needs the Game type in order to work. However, when I give process.c access to main.h (the file that Game is declared in) I get issues.
My code works fine when it's in one file. My header files are protected from duplication and are properly included in the program. The problem is, I need to include main.h in both main.c and process.c. And I have to include process.h in both 'main.c' and 'process.c'. I have tried every configuration and nothing works.
In some #include configurations I get no errors, but I get this weird message that says "It seems your project has not been built yet; would you like to build it now?" and when I click "Yes" nothing happens.
My compiler works fine and there is nothing wrong with the projects settings. What the heck is going on here? How do I get main.h and process.h to work together?
EDIT: Source code:
main.c:
#include <stdio.h>
#include "main.h"
#include "process.h"
void initGame(Game *thisGame)
{
variable = 10;
number = 5;
letter = 'c';
}
int main()
{
Game thisGame;
initGame(&thisGame);
displayData(&thisGame);
return 0;
}
main.h:
#ifndef _MAIN_H_
#define _MAIN_H_
typedef struct
{
int variable, number;
char letter;
}
#endif
process.c:
#include <stdio.h> //not sure if this should be here or not, it doesn't seem to effect my code
#include "main.h"
#include "process.h"
void displayData(Game *thisGame)
{
printf("%i, %i, %c", thisGame.variable, thisGame.number, thisGame.letter);
}
process.h:
#ifndef _MAIN_H_
#define _MAIN_H_
void displayData(Game *thisGame);
#endif
Error message
-------------- Build: Debug in FishKiller (compiler: GNU GCC Compiler)---------------
mingw32-g++.exe -L..\deps\lib -L..\SDLFILES\lib -o bin\Debug\FishKiller.exe obj\Debug\main.o obj\Debug\process.o -lmingw32 -lSDL2main -lSDL2 -lSDL2_image
obj\Debug\process.o:process.c:(.rdata+0x0): multiple definition of `SCREEN_WIDTH'
obj\Debug\main.o:main.c:(.rdata+0x0): first defined here
obj\Debug\process.o:process.c:(.rdata+0x4): multiple definition of `SCREEN_HEIGHT'
obj\Debug\main.o:main.c:(.rdata+0x4): first defined here
obj\Debug\process.o:process.c:(.rdata+0x8): multiple definition of `GAMESTATE_MENU'
obj\Debug\main.o:main.c:(.rdata+0x8): first defined here
obj\Debug\process.o:process.c:(.rdata+0xc): multiple definition of `GAMESTATE_GAME'
obj\Debug\main.o:main.c:(.rdata+0xc): first defined here
obj\Debug\process.o:process.c:(.rdata+0x10): multiple definition of `GAMESTATE_GAMEOVER'
obj\Debug\main.o:main.c:(.rdata+0x10): first defined here
collect2.exe: error: ld returned 1 exit status
Process terminated with status 1 (0 minute(s), 0 second(s))
0 error(s), 0 warning(s) (0 minute(s), 0 second(s))

Answer 1

Issues are address file by file below. Once these issues are corrected in your source, the executable will build.
1)
In process.h you have the wrong header blocks:
#ifndef _MAIN_H_
#define _MAIN_H_
//Change to:
#ifndef _PROCESS_H_
#define _PROCESS_H_
Also change:
void displayData(Game *thisGame);(see notes in main.h for explanation)
To:
void displayData(GAME *thisGame);
2) In process.c you have;
#include "main.h"
It does not hurt anything, but since we are analyzing everything, it is not needed to support current architecture.
You also have:
printf("%i, %i, %c", thisGame.variable, thisGame.number, thisGame.letter);
Because the thisGame is passed in as a pointer, you need to use struct pointer operator: ->
printf("%i, %i, %c", thisGame->variable, thisGame->number, thisGame->letter);
Also, the function protocol in the same file is incorrect. You are attempting to instantiate a variable type that does not exist: (see notes for main.h)
Change:
void displayData(Game *thisGame){...}
To:
void displayData(GAME *thisGame){...}//uses typedef struct GAME
3) in main.h you have a malformed struct:
typedef struct
{
int variable, number;
char letter;
}//no ";" statement terminator to indicate to your compiler _end of struct_
And with this definition, there is no struct name with which to reference or instantiate it in any other file. Change it to the following:
typedef struct
{
int variable;
int number;//style point , put each member on its own line
char letter;
}GAME;//note struct type name and terminator ";"
With the struct type name, in this case GAME, you can create instances of this struct in any file that #includes this file.
extern GAME Game;// using the extern modifier, create an instance of GAME
// that can be referenced in any file of the
//project, once initialized. (See the line GAME Game; in main.c)
4) in main.c you have variables in the function initGame that need to be referenced differently. Change this:
void initGame(Game *thisGame)
{
variable = 10;
number = 5;
letter = 'c';
}
To:
void initGame(GAME *thisGame)
{
thisGame->variable = 10;
thisGame->number = 5;
thisGame->letter = 'c';
}
There is Code::Blocks information here that may help you to set up your environment to get the error messages that will help you to debug your code.