MightyPork MightyPork - 3 months ago 26
C Question

Getopt not included? implicit declaration of function ‘getopt’

I wanted to use getopt, but it just won't work.

It's giving me

gcc -g -Wall -std=c99 -ftrapv -O2 -Werror -Wshadow -Wundef -save-temps -Werror-implicit-function-declaration -c -o src/main.o src/main.c
src/main.c: In function ‘main’:
src/main.c:13:2: error: implicit declaration of function ‘getopt’ [-Werror=implicit-function-declaration]
src/main.c:23:14: error: ‘optarg’ undeclared (first use in this function)
src/main.c:23:14: note: each undeclared identifier is reported only once for each function it appears in
src/main.c:26:9: error: ‘optopt’ undeclared (first use in this function)
src/main.c:28:5: error: implicit declaration of function ‘isprint’ [-Werror=implicit-function-declaration]
src/main.c:36:5: error: implicit declaration of function ‘abort’ [-Werror=implicit-function-declaration]
src/main.c:36:5: error: incompatible implicit declaration of built-in function ‘abort’ [-Werror]
src/main.c:43:15: error: ‘optind’ undeclared (first use in this function)
cc1: all warnings being treated as errors
make: *** [src/main.o] Error 1


Here's the source if you wanna see it
(almost exact copypasta from getopt manpage)

#include <stdio.h>
#include <unistd.h> // getopt
#include "myfn.h"

int main(int argc, char *argv[])
{

int aflag = 0;
int bflag = 0;
char *cvalue = NULL;
int c;

while((c = getopt(argc, argv, "abc:")) != -1) {

switch(c) {
case 'a':
aflag = 1;
break;
case 'b':
bflag = 1;
break;
case 'c':
cvalue = optarg;
break;
case '?':
if (optopt == 'c')
fprintf (stderr, "Option -%c requires an argument.\n", optopt);
else if (isprint(optopt))
fprintf (stderr, "Unknown option `-%c'.\n", optopt);
else
fprintf (stderr, "Unknown option character `\\x%x'.\n", optopt);

return 1;

default:
abort ();
}

}

printf ("aflag = %d, bflag = %d, cvalue = %s\n", aflag, bflag, cvalue);

for (int i = optind; i < argc; i++) {
printf ("Non-option argument %s\n", argv[i]);
}

return 0;
}


Any ideas what I'm doing wrong?

I'm on Linux, so I assumed it should work like this.

Answer

Try removing the -std=c99. This prevents the POSIX macros from being defined in <features.h>, which prevents <unistd.h> from including <getopt.h>. Or include getopt.h yourself.