changing variables within functions in other files

[mikeecb]

Hi guys, I am still new to using headers etc and keeping different classes and functions within different files. Basically, I thought that whenever you include "anotherfile.h" it is as if the function / classes within it are in the main file?

So if I have a few variables etc int a = 0, int b = 5 in the main file and I say whenever I want to call the function, change a and b (without having to make the file a int because i want to change many values, how do it do it.

Here is an example of the code i have:

in main file:

#include <iostream>
#include <stdlib.h>
#include <stdio.h>
#include <time.h>

#ifdef __APPLE__
#include <OpenGL/OpenGL.h>
#include <GLUT/glut.h>
#else
#include <GL/glut.h>
#endif

using namespace std;

#include "levelZero.h"

string squareFilled[200][100];

int main (int argc, char **argv){
    if (level[0] == true) {
        LevelZero levelZeroObject;
        levelZeroObject.floor();
    }
}

in levelZero.h:

#ifndef __BoxExpress__levelZero__
#define __BoxExpress__levelZero__

#include <iostream>
#include <stdlib.h>
#include <stdio.h>

using namespace std;

class LevelZero {
public:
    void floor();
};

#endif 

in levelZero.cpp:

#include "levelZero.h"

string squareFilled[200][100];
void LevelZero::floor() {
    squareFilled[50][50] = "vehicle";
}

Now how do I change the values of squareFilled in the main file from a different file? Any help would be much appreciated!

[mikeecb]

I changed the variable to a extern and it seems to be working now ! LEt me know if that is good practice!

[Peter87]

Global variables are often not considered good practice. Instead you could define squareFilled in main and pass it as argument to the floor function.

[mikeecb]

This is becoming more of a beginners c++ question, but I have tried passing string squareFilled[200][100] to the floor function but my compiler is just coming back with tons of errors. :/ How would you pass a two dimensional array?

[Peter87]

You have to add the array parameter to the function.
void floor(string squareFilled[200][100]);
You don't actually need to specify the first dimension.
void floor(string squareFilled[][100]);
or it could be written like this
void floor(string (*squareFilled)[100]);
All three ways will work exactly the same. The first two might look easier but the third more clearly shows that what is actually being passed is a pointer.

Another way to do it is to pass it by reference
void floor(string (&squareFilled)[200][100]);

When you call the function you pass the object as normal:
levelZeroObject.floor(squareFilled);

[mikeecb]

that works great. I was doing the same thing before but passing it to the wrong function i just realised! thanks a lot for your help!