Not able to call an extern function

Question

I want to call a function that reside in my func.c file into my main.c This is my func.c

#include "func.h"
int func(int i) {
return ++i ;
}

This is my header file func.h

int func(int i);

And this is my main code: main.c

#include <stdio.h>
#include <stdlib.h>
#include "func.h"    
main()
{
   int res = func(3);
   printf("%d\n",res);  
system("pause");
}

Compiling the main code I get the error: undefined reference to 'func' My goal is to call function from an external file (that is not part of the same compilation unit). How to do it? Thank you!

possible duplicate of [What is an undefined reference/unresolved external symbol error and how do I fix it?](http://stackoverflow.com/questions/12573816/what-is-an-undefined-reference-unresolved-external-symbol-error-and-how-do-i-fix) — Bartek Banachewicz, Dec 23 '14 at 10:14
You don't get an error while compiling. You get an error while *linking*. — Bartek Banachewicz, Dec 23 '14 at 10:14
Have you tried `#include "func.h"` instead of `#include ` in `main.c`? — David Ranieri, Dec 23 '14 at 10:14
@AlterMann Completely irrelevant. Headers files don't affect linkage in C. — The Paramagnetic Croissant, Dec 23 '14 at 10:18
@OP: You have to link together both files. Something like `gcc -o progname main.c func.c`. — The Paramagnetic Croissant, Dec 23 '14 at 10:19
or use `gcc -c main.c` if you'd wanted to do the linking in a separate step — Hans Z., Dec 23 '14 at 10:21
Disagree w the duplicate vote, that Q/A is so big that it is hard for OP to pick his/her problem out from all the other problems — M.M, Dec 23 '14 at 10:32
@MattMcNabb so hard to copy-pasta the error message verbatim into Google, right? — The Paramagnetic Croissant, Dec 23 '14 at 10:36
@TheParamagneticCroissant re. your comment on the now-deleted post: if a `#include` directive cannot open the file named in the directive then compilation should fail. There's no "optional includes" in C. (well - the standard doesn't say that unambiguously, but all compilers behave that way). — M.M, Dec 23 '14 at 11:51

score -2 · Answer 1 · answered Dec 23 '14 at 10:27

-2

#include <stdio.h>
#include <stdlib.h>
#include "func.h"    // change ( since func.h is not a slandered header file its a user define header file)  
main()
{
   int res = func(3);
   printf("%d\n",res);  
system("pause");
}

answered Dec 23 '14 at 10:27

rabi shaw

441
1
3
14

1

The inclusion of the header file has nothing to do with the linker error. It won't cause it, it won't resolve it. – The Paramagnetic Croissant Dec 23 '14 at 10:29
as you mentioned in your earlier comments that we can link both the file using gcc -o progname main.c func.c or or use gcc -c main.c but if you try to compile using any of these you will hit the error "func.h no such file or dir" – rabi shaw Dec 23 '14 at 10:34
2

This does not provide an answer to the question. To critique or request clarification from an author, leave a comment below their post - you can always comment on your own posts, and once you have sufficient [reputation](http://stackoverflow.com/help/whats-reputation) you will be able to [comment on any post](http://stackoverflow.com/help/privileges/comment). – DavidPostill Dec 23 '14 at 10:47
@DavidPostill Where do you see the request for clarification? – Tom Dec 23 '14 at 11:41
@Tom It is the default text that is added when flagging an answer that doesn't answer the question but may be a valid comment ... – DavidPostill Dec 23 '14 at 11:57
@DavidPostill I know that this is a standard text and I still don't know why you've choosed that and why this is not an answer. It might be a bad one, but still an "answer". – Tom Dec 23 '14 at 12:01
It doesn't help either. – user3789035 Dec 23 '14 at 12:02
@Tom I didn't flag it as "not an answer". That is a different flag. I flagged it because it doesn't actually answer the question, but it **could** be a valid **comment**. – DavidPostill Dec 23 '14 at 12:05
@DavidPostill Well, when you can explain why it doesn't answer the question? – Tom Dec 23 '14 at 12:11
@Tom Please see the rest of the comments and the edit to the question. `#include "func.h"` hasn't fixed the problem ... – DavidPostill Dec 23 '14 at 12:15
@DavidPostill And? As I said, it might be a bad/wrong answer and it might deserve downvotes for that, but this doesn't justify the flags. I guess we both have different opinions in that case and won't get an agreement. – Tom Dec 23 '14 at 12:25

Not able to call an extern function

1 Answers1