Use variables from one program in another

Question

I am creating two 2D arrays in one file, say readbundle.cpp. They are quite huge in dimension, as they actually 3D points created from an image, after some heavy mathematics.

Now, how can I use the values from here, in another file, resectioning.cpp? I know this uses the concept of oops and classes. But if you can just temme the probable syntax and how to use them, it would be really helpful. Please help me here. Thanks in advance. I have searched in google, but since I am new to this,I am not sure what am I looking at or where to look. My apologies if you feel this is very rudimentary.

The code is in c++.

They are 2 different files totally. I haven't made them a same program or created any class. This is what I want to know. How to connect them, and how to use the values from one in another.

Suppose X[i][j] is just normally created and defined in readbundle.cpp and after compiling and executing it, I have certain values in X[i][j].

Now I want to use this X[i][j] in the program, resectioning.cpp, which I am compiling separately. I haven't defined any class, or any oops. Please help me how can I achieve this. These two programs aren't connected as of now. They are just normal programs. I know I have to do something public and call the variable somehow. But I just dunno the right way of doing it. Please correct me if am wrong as well.

Edit

suppose the readbundle.cpp is as follows

    #include ...
    .
    . 
    vector<vector<int> >X3D;(declared global)
    .
    .

and the resect.cpp is as follows

    #include ....
    .
    .
    .
    extern vector<vector<int> >X3D //will the values be reflected here?
    //the values changed in *readbundle.cpp*

    int main()
    {
          cout<<X3D[0][0]<<endl;
    }

From the answers, I hope I understood the concept of extern correct. Please help me if am wrong.

NOTE Will I get the same values X3D from the previous file? Am getting an error in this case. How can I achieve the functionality am looking for?

Answer 1

You can do this like this:

In your arrayfile you declare the array however it looks like, i.E.

char MyArray[] = { 123, 20, -4, ...};
unsigned int MyArraySize = sizeof(MyArray);

In your sourcefile you can reference it like this:

extern char MyArray[];
extern unsigned int MyArraySize;

If you know the size in advance you can do

char MyArray[10] = ...;

and

extern char MyArray[10];

Update

Here is a sample code to get you started. Create the files as indicated. If you change the names don't forget to change the include directive as well. ;)

ArrayFile.h:

#ifndef ARRAYFILE_H_
#define ARRAYFILE_H_

#define ARRAY_ROWS      5
#define ARRAY_COLUMNS   3


#endif /* ARRAYFILE_H_ */

ArrayFile.cpp:

#include "ArrayFile.h"

char BundleArray[ARRAY_ROWS][ARRAY_COLUMNS] =
{
    { 1, 2, 3 },
    { 2, 4, 5 },
    { 3, 6, 7 },
    { 4, 8, 9 },
    { 5, 0, 6 },
};

ArraySample.cpp

#include <iostream>

#include "ArrayFile.h"

extern char BundleArray[ARRAY_ROWS][ARRAY_COLUMNS];

int main()
{
    unsigned int rows = ARRAY_ROWS;
    unsigned int columns = ARRAY_COLUMNS;

    for(unsigned int x = 0; x < rows; x++)
    {
        std::cout << "Row:" << x << std::endl;
        for(unsigned int y = 0; y < columns; y++)
        {
            std::cout << "Value [" << x << "/" << y << "] = " << (char)((BundleArray[x][y])+0x30) << std::endl;
        }
    }
    return 0;
}

When you created these files, compile them.

Answer 2

I assume that the two files you mention are both source files and you want to complile them seperately and run them as part of the same program.

Look into how your linker works and have a look at static variables.