Linking .c and .h files

Question

For my program I am linking 3 files in total. A main.c, sortfile.c and my.h(header file). For my sortfile.c I am implementing a OddEven Sort. I am unsure whether my coding algorithm is correct. Also would like to know what information usually goes in a header file. Is it only the other two c files vide #include?

#include <stdio.h>


void swap(int *, int *);
void Odd_Even_Sort(int *);


/* swaps the elements */
void swap(int * x, int * y)
{
    int temp;

    temp = *x;
    *x = *y;
    *y = temp;
}

/* sorts the array using oddeven algorithm */
void Odd_Even_Sort(int * x)
{
    int sort = 0, i;

    while (!sort)
    {
        sort = 1;
        for (i = 1;i < MAX;i += 2)
        {
            if (x[i] > x[i+1])
            {
                swap(&x[i], &x[i+1]);
                sort = 0;
            }
        }
        for (i = 0;i < MAX - 1;i += 2)
        {
            if (x[i] > x[i + 1])
            {
                swap(&x[i], &x[i + 1]);
                sort = 0;
            }
        }
    }

I did not include a main in the sortfile.c because I intended to put main in the main.c file.

Answer 1

You look confused. Read first the wikipage on linkers and on compilers. You don't link source files, but only object files and libraries.

^{(I am guessing and supposing and hoping for you that you are using Linux)}

You also compile translation units into object files.

Header files are for the preprocessor (the first "phase" of the compilation). The preprocessing is a textual operation. See this answer for some hint.

So you probably want to compile your main.c into main.o with

gcc -Wall -g -c main.c -o main.o

(the -Wall asks for all warnings, so never forget that; the -g asks for debugging information; -c asks to compile some source into some object file; order of program arguments to gcc matters a big lot).

Likewise, you want to compile your sortfile.c into sortfile.o. I leave as an exercise to get the right command doing that.

Finally, you want to get an executable program myprogsort, by linking both object files. Do that with

gcc -g main.o sortfile.o -o myprogsort

But you really want to use some build automation tool. Learn about GNU make. Write your Makefile (beware, tabs are important in it). See this example. Don't forget to try make -p to understand (and take advantage of) all the builtin rules make is knowing.

Also would like to know what information usually goes in a header file.

Conventionally you want only declarations in your common header file (which you would #include in every source file composing a translation unit). You can also add definitions of static inline functions. Read more about inline functions (you probably don't need them at first).

Don't forget to learn how to use the gdb debugger. You probably will run

gdb ./myprogsort

more than once. Don't forget to rebuild your thing after changes to source code.

Look also inside the source code of some medium sized free software project coded in C on github. You'll learn a big lot.