Extending array to source file from header file in C

Question

Is there a way to extend one really big array from header file to source file, and use his elements in main program?

array like this

BYTE codes[95][8] = {            
255, 255, 255, 255, 255, 255, 255, 255, 
255, 255, 134, 255, 255, 255, 255, 255, 
255, 143, 255, 143, 255, 255, 255, 255, 
235, 128, 235, 143, 235, 255, 255, 255, 
237, 213, 128, 213, 219, 255, 255, 255, 
157, 155, 247, 226, 220, 255, 255, 255, 
201, 112, 170, 221, 250, 255, 255, 255, 
255, 175, 129, 255, 255, 255, 255, 255, 
255, 227, 221, 190, 255, 255, 255, 255, 
255, 190, 221, 227, 255, 255, 255, 255, 
235, 247, 193, 247, 235, 255, 255, 255, 
247, 247, 193, 247, 247, 255, 255, 255, 
255, 250, 249, 255, 255, 255, 255, 255, 
247, 247, 247, 247, 247, 255, 255, 255, 
255, 252, 252, 255, 255, 255, 255, 255, 
253, 251, 247, 239, 223, 255, 255, 255, 
193, 186, 182, 174, 193, 255, 255, 255, 
255, 222, 128, 254, 255, 255, 255, 255, 
222, 188, 186, 182, 206, 255, 255, 255, 
189, 190, 174, 150, 185, 255, 255, 255, 
};

Answer 1

What is

"extend .... from header file to source file"?

If I understood correctly, you want to access the codes array from the source file. For that you need to #include the header file to the source file and make use of the array codes. Remember, it will be in global scope (if that matters).

Having said that, as metioned in the other answer by Mr. Lundin the best approach is to

• Declare the variable(s) [which needs to be used across several translation units (source files)] in the header file.
• Define the variable(s) in one of the sopurce files.
• #include the header file in all the source files and make use of the variable.

Answer 2

It's not a good idea to put data like this in a header file.

Include guards will not prevent the array from being re-defined in multiple compilation units. This will wreak havoc with the link stage.

Put it in a source file instead and use extern if multiple compilation units require codes.

Answer 3

Never define any variables in header files. It creates linker problems and is bad program design. Instead, this array should be declared as

const BYTE codes[95][8] = { ...

and placed in a .c file. You can then have a corresponding .h file with

extern const BYTE codes[95][8];

Include the .h file from the caller and you will get access to the array.

Answer 4

If I understand correctly you want to define part of the array initializer list in one file and have the remainder of the initializer list in another file.

This is a case where, yes, you can do that - but IMO you probably don't want to. I think it's brittle, prone to failure, awkward to maintain, and for myself I can't picture why this would be needed. However, if you insist, here's an implementation of how it can be done:

array_test.h

unsigned char codes[95][8] = {            
  255, 255, 255, 255, 255, 255, 255, 255, 
  255, 255, 134, 255, 255, 255, 255, 255, 
  255, 143, 255, 143, 255, 255, 255, 255, 
  235, 128, 235, 143, 235, 255, 255, 255, 
  237, 213, 128, 213, 219, 255, 255, 255, 
  157, 155, 247, 226, 220, 255, 255, 255, 
  201, 112, 170, 221, 250, 255, 255, 255, 
  255, 175, 129, 255, 255, 255, 255, 255, 
  255, 227, 221, 190, 255, 255, 255, 255, 
  255, 190, 221, 227, 255, 255, 255, 255, 
  235, 247, 193, 247, 235, 255, 255, 255, 
  247, 247, 193, 247, 247, 255, 255, 255, 
  255, 250, 249, 255, 255, 255, 255, 255, 
  247, 247, 247, 247, 247, 255, 255, 255, 
  255, 252, 252, 255, 255, 255, 255, 255, 
  253, 251, 247, 239, 223, 255, 255, 255, 
  193, 186, 182, 174, 193, 255, 255, 255, 
  255, 222, 128, 254, 255, 255, 255, 255, 
  222, 188, 186, 182, 206, 255, 255, 255, 
  189, 190, 174, 150, 185, 255, 255, 255, 

array_test.c

#include <stdio.h>

#include "array_test.h"

  247, 247, 193, 247, 247, 255, 255, 255, 
  255, 250, 249, 255, 255, 255, 255, 255, 
  247, 247, 247, 247, 247, 255, 255, 255, 
  255, 252, 252, 255, 255, 255, 255, 255, 
  253, 251, 247, 239, 223, 255, 255, 255, 
  193, 186, 182, 174, 193, 255, 255, 255, 
  255, 222, 128, 254, 255, 255, 255, 255, 
  222, 188, 186, 182, 206, 255, 255, 255, 
  189, 190, 174, 150, 185, 255, 255, 255 
  };

int main(int argc, char **argv)
  {
  printf("whatever\n");
  }

Note that the initializer list for codes is not terminated in array_test.h (in other words, there's no }; at the end of the initalizer list for codes), so the continuation of the list must immediately follow the include of "array_test.h". It also makes the program look odd - when looking at array_test.c the continuation of the initializer list appears to be syntactically incorrect, and yet it compiles (using cc array_test.c on HP-UX). I don't recommend doing this - but it's an interesting case I had not thought of before.

Best of luck.