Working with multiple source files

I've seen you all working with multiple source files and I want to do it too!

I have

main.c
function1.c
function2.c

Now how do I link them together? I mean do I have to add something in main.c to include the other two files or what and how to do that? I am using command line to compile.
Someone told me to do

Code:

---

gcc main.c function1.c function2.c -o executable

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And some other random guy told me to

Code:

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#include "function1.c"
#include "function2.c"

---

in main.c But both give me 200 errors (probably some of them are syntax errors)

Anyway, which is the correct way to do this?

Thanks

> And some other random guy told me to...
No :)

Put the prototypes of the functions you want to use from function1.c into function1.h (Or whatever) and include that in main.c

ie

Code:

---

#include "function1.h"

int main(void)
{
    hello_world();
    return 0;
}

---

function1.h

Code:

---

void hello_world(void);

---

function1.c

Code:

---

#include <stdio.h>

void hello_world(void)
{
    printf("Hello world\n");
}

---

Code:

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gcc main.c function1.c -o executable

---

Note: don't compile the header files

Also you may want to google "Inclusion guards"

You can also use global variables from other source files by using the keyword "extern"

For example if function1.c looks like this:

Code:

---

int function1Test = 0;

---

and you want to access the variable "function1Test" from another .c file than in function1.h put

Code:

---

extern int function1Test;

---

main.c

Code:

---

#include "function1.h"

int main()
{
  function1Test = 32;
  return 0;
}

---

Yes but I wouldn't recommend abusing them :)

Quote:

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Originally Posted by zacs7

function1.h

Code:

---

void hello_world(void);

---

function1.c

---

Can I put both function prototypes in 1 header file or I have to make n number of header files for n number of functions?

Quote:

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Originally Posted by 39ster

You can also use global variables from other source files by using the keyword "extern"

---

Yeah thanks, I think that will fix those 200 errors :D

Quote:

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Originally Posted by abh!shek

Can I put both function prototypes in 1 header file or I have to make n number of header files for n number of functions?




Yeah thanks, I think that will fix those 200 errors :D

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You can but it's better to have one header for each .c file. It's more organised.

Thanks zacs7 and 39ster :)

Just don't forget to compile and link each of the source files, or you will (likely) get errors!

Quote:

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Originally Posted by 39ster

You can but it's better to have one header for each .c file. It's more organised.

---

Although sometimes it makes sense to have one header file for a bunch of source files that provide some particular functionality. E.g. you may have "jpeg.h" for the source files "jpegreadwrite.c", "jpegcompression.c", "jpeginfo.c", "jpegdrawing.c".

This particularly make sense if your jpeg*.c files become a "libjpeg" library.

--
Mats

Quote:

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Originally Posted by Elysia

Just don't forget to compile and link each of the source files, or you will (likely) get errors!

---

lolz I _am getting_ errors :p

I don't know how to link or anything. I just know I have to do gcc sourcefile1.c source2.c -o executable

How do I link?

I'm getting errors like

* printf, scanf undeclared in function1
* The macros(?) I defined with #define are undeclared and stuff like that!

Command lines are beyond me.
The errors you get suggests that you have failed to link with the standard library for the compiler.

Quote:

---

Originally Posted by abh!shek

lolz I _am getting_ errors :p

I don't know how to link or anything. I just know I have to do gcc sourcefile1.c source2.c -o executable

How do I link?

I'm getting errors like

* printf, scanf undeclared in function1
* The macros(?) I defined with #define are undeclared and stuff like that!

---

To fix your problems with printf/scanf, you need to include <stdio.h> in the file that uses those functions. Likewise, if you have #define, they need to be in an include file that is included by the file that uses the #define.

To separately compile, use individual file compilation:

Code:

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gcc -c somefile.c
gcc -c otherfile.c

---

then link with:

Code:

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gcc -o executable somefile.o otherfile.o

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You should probably also use

Code:

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gcc -Wall ...

---

as that will give you warnings whenever you do something that may be a bit wrong.

--
Mats

Quote:

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Originally Posted by matsp

Although sometimes it makes sense to have one header file for a bunch of source files that provide some particular functionality. E.g. you may have "jpeg.h" for the source files "jpegreadwrite.c", "jpegcompression.c", "jpeginfo.c", "jpegdrawing.c".

This particularly make sense if your jpeg*.c files become a "libjpeg" library.

--
Mats

---

Yeah i like to use 1 header for libs and dlls

Putting it all in one header may also bloat it.
So plan carefully.

Quote:

---

Originally Posted by Elysia

Putting it all in one header may also bloat it.
So plan carefully.

---

Sure - there's all sorts of different reasons to have different solutions - I was just trying to point out that sometimes it's not the ideal solution to have one header for each source file - it often is, but not always.

--
Mats

I have a similar question so I thought I would necro this thread.

I'm a math student trying to write a program so I don't know too much. I'm working on fedora code 5.
I am trying to make a call to a C program called nauty (it calculates automorphism groups of graphs).
As a first step I'm just trying to run one of it's example programs, which executes a simple call to nauty.
However it says "It needs to be linked with nauty.c nautil.c and naugraph.c.".
I've got a vague idea of what that means from reading around here a little bit.
When I try to compile my example program I get a whole host of errors. It seems that the example cannot find nauty. This isn't too suprising since nauty is in a different folder.

So my question is: how do I link my example program to other c files that are located elsewhere?

Here is the example program in full.
The nauty files are in /usr/local/nauty22

Code:

---

/* This program prints generators for the automorphism group of an
  n-vertex polygon, where n is a number supplied by the user.
  It needs to be linked with nauty.c, nautil.c and naugraph.c.
  This version uses a fixed limit for MAXN.
*/
#define MAXN 100
#include "nauty.h"  /* which includes <stdio.h> */
main()
{
    graph g[MAXN*MAXM];
    int lab[MAXN],ptn[MAXN],orbits[MAXN];
    static DEFAULTOPTIONS(options);
    statsblk(stats);
    setword workspace[50*MAXM];
    int n,m,v;
    set *gv;
    options.writeautoms = TRUE;
    while (1)
    {
        printf("\nenter n : ");
        if (scanf("%d",&n) == 1 && n > 0)
        {
            if (n > MAXN)
            {
                printf("n must be in the range 1..%d\n",MAXN);
                exit(1);
            }
            m = (n + WORDSIZE - 1) / WORDSIZE;
            nauty_check(WORDSIZE,m,n,NAUTYVERSIONID);
            for (v = 0; v < n; ++v)
            {
                gv = GRAPHROW(g,v,m);
                EMPTYSET(gv,m);
                ADDELEMENT(gv,(v+n-1)%n);
                ADDELEMENT(gv,(v+1)%n);
            }
            printf("Generators for Aut(C[%d]):\n",n);
            nauty(g,lab,ptn,NULL,orbits,&options,&stats,
                                            workspace,50*MAXM,m,n,NULL);
        }
        else
            break;
    }
}

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Hopefully I havn't broken any protocal here.
Thanks very much for any and all advice.

You would type "gcc" followed by all the .c files needed to make a complete program. If they are in different directories, you can specify a path to those files, or move all the .c files so they are together.

Thanks very much, I appreaciate it ^^