Function declaration in static library in C

Question

I've a problem when I try to compile my program with my static library. I create the object file of my .c files whith gcc -c ft_putstr.c. Then I execute ar -rcs libft.a ft_putstr.o and then I make gcc main.c -L. -lft and I've

warning: implicit declaration of function 'ft_putstr' is invalid in C99.

The binary is created but I don't want this warning even if it's work like that. It works if I had the flag -std="c89" on GCC but I have tu use C99.

This is my main :

int main(void)
{
     ft_putstr("Bonjour");
     return (0);
}

This my ft_putstr.c :

#include <unistd.h>

    void    ft_putstr(char *str) 
    {
         (*str) ? write(1, str, 1), ft_putstr(str + 1) : 0; 
    }

Do you import `ft_putstr.h` from `main.c`? Does that header define the function? — sapi, Aug 11 '14 at 09:52
No, I don't import it because I've seen a video (given by my school) which make work the program without any .h. I've already tried with a .h and yes it works. — sebasthug, Aug 11 '14 at 09:54
The problem is that `main()` cannot see it. Put it in a header and include it in the file with `main()` If you can't import a header, then just declare it static extern in one file and include the prototype in the file with `main` — David C. Rankin, Aug 11 '14 at 09:54
Without declaring `ft_putstr`, you're always going to get an implicit declaration warning. Hell, you could declare it in main.c if you want (please don't though; that'd be stupid). — sapi, Aug 11 '14 at 09:55
I think than you have a very higher level than the mine so I will add a header file, this is the better option I think now. Many thanks for your help and sorry if I was unpleasant. It does more than 2 hours than I'm on it. — sebasthug, Aug 11 '14 at 09:59
You will need to declare the function in one file completely. In your case it is not declared in the file with main. Then in the file with main add a `extern` declaration. (i.e. `extern void ft_putstr(char *str);` — David C. Rankin, Aug 11 '14 at 10:07
@sapi declaring it in main.c is slightly better than not declaring it at all — M.M, Aug 11 '14 at 11:29

score 5 · Accepted Answer · edited Aug 11 '14 at 10:05

5

You should include a header file which has a declaration like

void    ft_putstr(char *str);

or you can insert this line in your main.c

extern void    ft_putstr(char *str);

edited Aug 11 '14 at 10:05

Jonathan Wakely

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answered Aug 11 '14 at 09:57

Jeegar Patel

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`extern` is superfluous here, all function declarations are extern unless you specifically indicate `static`. – M.M Aug 11 '14 at 11:30

Function declaration in static library in C

1 Answers1