"implicit declaration of function" in utarray.h (part of uthash)

Question

I'm using utarray (part of the uthash library) for a project. Whenever I include it, I get the following error:

utarray.h:221:3: error: implicit declaration of function ‘strdup’ [-Wimplicit-function-declaration]

Admittedly, I use some pretty aggressive flags when compiling (-Wall -Wpedantic -Wextra -Werror -pedantic-errors -std=c99), but I don't understand why this should be an error at all. strdup is defined in string.h (according to man strdup) which is very clearly included from utarray.h.

What am I doing wrong? Google was no help. (apparently nobody else tries to compile utarray.h with these flags?)

Here's an example file that fails to compile (using gcc -Wall -Wpedantic -Wextra -Werror -pedantic-errors -std=c99 scratch.c).

#include "utarray.h"

int main(int argc, char *argv[]) {
    (void)argc;
    (void)argv;
    return 0;
}

versions: gcc 4.9.2, glibc 2.21, uthash 1.9.9

Answer 1

The problem is that strdup() is not a c standard function it's a POSIX function, you can't use -std=c99 when you use strdup() unless you add the following -D_POSIX_C_SOURCE=200809L to the compilation command

gcc -Wall -Wpedantic -Wextra -Werror -pedantic-errors -std=c99 -D_POSIX_C_SOURCE=200809L

Answer 2

I had the same error with strdup), so I added the dummy prototype statement

char * strdup(char *) ; 

I don’t get the error message anymore.