Using one .hh files for multiple .cc files

[UofCRussell]

I will give the general idea here, I am taking a Software development class (im a computer engineering student) and I have run into a road block (could be the coffee and the fact that I am sick) but I want to use 1 .hh file (define.hh) to store a bunch of variable information for about 6 or 7 other files. The problem that I am having is that I am getting multiple defines, how do I get around this problem? (the point of all of this is so that I only have to change one file rather then 5 .hh files)

[Roonie]

try

#ifndef _PICK_A_NAME
#define _PICK_A_NAME
. . .
#endif

[UofCRussell]

try

#ifndef _PICK_A_NAME
#define _PICK_A_NAME
. . .
#endif

Yeah I dont under stand why that is not working! Here is my code:

#ifndef DEFINE_VAR_HH
#define DEFINE_VAR_HH


//NEEDED INCLUDE FILES
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <stdio.h>
#include <unistd.h>
#include <pthread.h>
#include <math.h>

//OPEN GL INCLUDE FILES FOR MAC
#include <GLUT/glut.h>
#include <OpenGL/glext.h>
#include <OpenGL/gl.h>
#include <OpenGL/glu.h>



//DEFINE NEEDED CONSTANTS
#define find_max_or_min(testvalue) \
{ \
if (testvalue > paddle_max) { testvalue = paddle_max; } \
else if (testvalue < paddle_min) { testvalue = paddle_min; } \
}

#define PI 3.14159265359

//NEEDED GLOBAL VARIABLES

//SET ALL GAME VARIABLES AND WINDOW SETTINGS
GLfloat screen_length = 400;
GLfloat screen_height = 425;
GLfloat number_of_players = 2;
GLfloat content_space = 25;

//SET VARIABLES FOR WALL DEVELOPMENT
GLfloat NUM_PARTS_WALL = 2;
GLfloat wall_height = 10;
GLfloat wall_length = 370;
GLfloat wall_x_position = 10;
GLfloat wall_border= 10;
GLfloat wall_red = 0.0;
GLfloat wall_blue = 0.0;
GLfloat wall_green = 1.0;

//SET VARIABLES FOR PADDLE DEVELOPMENT
GLfloat paddle_height = 75;
GLfloat paddle_length = 10;
GLfloat paddle_x_position = 0;
GLfloat paddle_y_position = 0;
GLfloat paddle_red = 0.40;
GLfloat paddle_blue = 0.85;
GLfloat paddle_green = 0.0;

//SET VARIABLES FOR BALL DEVELOPMENT
GLfloat ball_radius = 7;
GLfloat ball_x_position = 0;
GLfloat ball_y_position = 0;
GLfloat ball_red = 1;
GLfloat ball_green = 1;
GLfloat ball_blue = 1;

#endif

The game is PONG!

[UofCRussell]

late night bumb

[Banfa]

Your problem is all your lines of this type

GLfloat screen_length = 400;
 

This defines and initialises the variable screen_length. Since this is a header file and gets included into many cc files the all get screen_length defined in them and you get a multiple definition error.

In header files you should only declare data not define it. A declaration tells the compiler that the variable exists somewhere in the program (it is the linkers job to work out where) where as a definition actually creates the variable.

You can not initialise in a declaration and you show it is a declaration by putting extern in front of it. So your header file should contain

extern GLfloat screen_length;
 

to declare the variable screen_length. There is more to do, if you only do this then you will have declared the variable in all your cc files but defined it no where. You will get an unresolved external symbol in the linker.

In 1 cc file (some people create 1 specially for this purpose an some just choose an existing cc file) you have to add you definitions so you would put

GLfloat screen_length = 400;
 

into a c file. The linker will link the variable declared in all the other cc files to the 1 definied in this 1 file.


Obviously you will have to do this for all the variables you have declared.

[UofCRussell]

That worked, thanks for the help! Great website, how you guys will be getting all my coding problems haha