How to link main with made libraries?

Question

I'm trying to link libraries I made to main source code, but it throws this error. I've been searching for last two hours how to fix this but nothing worked for me.

Compiling:

cd "c:\Users\miros\OneDrive\Documents\C codes\labovi"
gcc 01main.c -o 01main
.\01main

d:/programs/mingw/bin/../lib/gcc/mingw32/9.2.0/../../../../mingw32/bin/ld.exe: C:\Users\miros\AppData\Local\Temp\ccGHtHKg.o:01main.c:(.text+0x46): undefined reference to 'faktorijel' d:/programs/mingw/bin/../lib/gcc/mingw32/9.2.0/../../../../mingw32/bin/ld.exe: C:\Users\miros\AppData\Local\Temp\ccGHtHKg.o:01main.c:(.text+0x72): undefined reference to 'suma' collect2.exe: error: ld returned 1 exit status

01ucitavanje.h

#ifndef UCITAVANJE_H
#define UCITAVANJE_H
#include <stdio.h>
#include <stdlib.h>

long long *niz;
int n;

void ucitavanje();
#endif

01ucitavanje.c

#include "01ucitavanje.h"

void ucitavanje(){
    scanf("%d", &n);
    niz = malloc(sizeof(long long) * n);
    for (int i = 0; i < n; i++)
        scanf("%d", niz + i);
}

01izracunavanje.h

#ifndef IZRACUNAVANJE_H
#define IZRACUNAVANJE_H
#include <stdio.h>

long long faktorijel(int n);
long long suma(long long *niz, int n);

#endif

01izracunavanje.c

#include "01izracunavanje.h"

long long faktorijel(int n){
    long long f;
    for (int i = 2; i <= n; i++)
        f *= i;

    return f;
}

long long suma (long long *niz, int n){
    long long s = niz[0];
    for (int i = 1; i < n; i++)
        s += niz[i];
    return s;    
}

main.c

#include "01izracunavanje.h"
#include "01ucitavanje.h"

int main(){
    ucitavanje();
    for (int i = 0; i < n; i++)
        niz[i] = faktorijel((int)niz[i]);
    printf("%d", suma(niz, n));
    free(niz);
    return 0;    
}

[link](https://gcc.gnu.org/onlinedocs/gcc/Link-Options.html) — ryyker, Mar 15 '21 at 15:16
I'm running it just the way I would run one .c file, meaning I'm trying to start main.c. — qu4lizz, Mar 15 '21 at 15:21
Have a look at this guide https://renenyffenegger.ch/notes/development/languages/C-C-plus-plus/GCC/create-libraries/index — Marco Frau, Mar 15 '21 at 15:26
You generally need to tell the linker how to find your libraries. Often, this would entail passing `-l` flags to the tool chain. — William Pursell, Mar 15 '21 at 15:30

score 4 · Accepted Answer · answered Mar 15 '21 at 15:34

4

You're compiling only main.c into the executable, so the other functions aren't available.

You need to compile each source file into an object file, then link the object files together.

gcc -c main.c
gcc -c 01izracunavanje.c
gcc -c 01ucitavanje.c
gcc -o 01main main.o 01izracunavanje.o 01ucitavanje.o

answered Mar 15 '21 at 15:34

dbush

205,898
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I did what you said here but program still doesn't run. Anything else to do? – qu4lizz Mar 15 '21 at 15:46
@qu4lizz Define "doesn't run". – dbush Mar 15 '21 at 15:47
I mean nothing happens. – qu4lizz Mar 15 '21 at 15:47
@qu4lizz So when you compile the program there's no output? – dbush Mar 15 '21 at 15:48
Yeah, even when I run .exe file, nothing. – qu4lizz Mar 15 '21 at 15:50
@qu4lizz That's a different problem. Time to do some debugging. – dbush Mar 15 '21 at 15:51
LMAO, I didn't have any output before input, so that's reason. Thank you! – qu4lizz Mar 15 '21 at 16:17

score 3 · Answer 2 · answered Mar 15 '21 at 15:34

3

I'm going to give you a mid-line correction because you put your compilation on one very long line.

In this case, you pass all your .c files to gcc. From

{ gcc 01main.c -o 01main }

We'd rather write

{ gcc -o 01main 01main.c 01izracunavanje.c 01ucitavanje.c }

Since you're not actually building a distribution library but rather a bunch of source files we just compile them all together. It generates better code that way anyway once you start optimizing.

Order of .c files doesn't really matter, but the file containing main is first by tradition. Putting -o before the first .c file used to matter and most people still do it.

answered Mar 15 '21 at 15:34

Joshua

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How to run program after doing this? – qu4lizz Mar 15 '21 at 15:47
@qu4lizz: I'm confused. Why is your `.\01main` not correct. – Joshua Mar 15 '21 at 17:06
Everything's right, I made a little mistake. Thanks anyway. – qu4lizz Mar 15 '21 at 19:41

How to link main with made libraries?

2 Answers2