faccessat and AT_* defines are undefined - c

Question

// SYSTEM INCLUDE FILES
#include <sys/types.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/uio.h>
// C STANDARD LIBRARY INCLUDE FILES
#include <errno.h>
#include <stdio.h>
#include <stddef.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
int main(int argc, char *argv[])
{
char *source = "file1.txt";
char *dest = "file2.txt";
printf("%d\n", faccessat(AT_FDCWD, source, F_OK | R_OK | W_OK, AT_SYMLINK_NOFOLLOW));
printf("%d\n", faccessat(AT_FDCWD, dest, F_OK | R_OK | W_OK, AT_SYMLINK_NOFOLLOW));
printf("Value of errno: %s\n", strerror(errno));
return 0;
}
When compiling this code with clang 14 and the command clang -lrt -pthread -I/usr/include -std=c11 -o copy copy.c I run into numerous issues:
copy.c:21:20: warning: implicit declaration of function 'faccessat' is invalid in C99 [-Wimplicit-function-declaration]
printf("%d\n", faccessat(AT_FDCWD, source, F_OK | R_OK | W_OK, AT_SYMLINK_NOFOLLOW));
^
copy.c:21:30: error: use of undeclared identifier 'AT_FDCWD'
printf("%d\n", faccessat(AT_FDCWD, source, F_OK | R_OK | W_OK, AT_SYMLINK_NOFOLLOW));
^
copy.c:21:68: error: use of undeclared identifier 'AT_SYMLINK_NOFOLLOW'
printf("%d\n", faccessat(AT_FDCWD, source, F_OK | R_OK | W_OK, AT_SYMLINK_NOFOLLOW));
^
copy.c:22:30: error: use of undeclared identifier 'AT_FDCWD'
printf("%d\n", faccessat(AT_FDCWD, dest, F_OK | R_OK | W_OK, AT_SYMLINK_NOFOLLOW));
^
copy.c:22:66: error: use of undeclared identifier 'AT_SYMLINK_NOFOLLOW'
printf("%d\n", faccessat(AT_FDCWD, dest, F_OK | R_OK | W_OK, AT_SYMLINK_NOFOLLOW));
^
1 warning and 4 errors generated.
The same code works on my Mac with MacOS 12, but does not work on Ubuntu in WSL. How would I fix this issue?
I tried to reinstall build-essentials, clang, gcc, glibc. I reviewed the header files and found that fcntl.h does not contain the AT_* definitions, yet the man page says they do. I was expecting the header file to contain the definitions.

Answer 1

From what the comments have told me, and online, faccessat is a gnu extension in C, so to use it I would have to compile my code with -std=gnu11 to use these.