unlinkat() a Directory in C - c

Question

I need to delete a directory in a given path using unlinkat(), the program runs fine but it doesn't delete (unlink) the directory (is empty by the way). Using the man7 documentation for unlinkat() I have the following code:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <time.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <pwd.h>
#include <grp.h>
#include <dirent.h>
#include <fcntl.h>
void main(int argc,char *argv[]){
DIR *dirp;
if ((dirp = opendir(argv[1]))== NULL){
fprintf(stderr, "Couldn't open the directory %s: %s \n",argv[1],strerror(errno) );
exit(1);
}
unlinkat(dirp,argv[1],AT_REMOVEDIR);
exit(0);
}
The path given in the arguments is relative from the father of the folder I want to erase

Answer 1

Your dirp is a pointer to a directory handle (DIR *), but the first argument to unlinkat() must be a directory descriptor, or AT_FDCWD (for "current working directory"). This is clearly stated in the unlinkat() man page.
You should always enable compiler warnings (-Wall for gcc). It would have pointed you to the problem in this case, too.
To get hold of the underlying descriptor for dirp, use dirfd(dirp).
Here is an actual example. It removes the (empty) directories specified in the second and further parameters, relative to the directory/path specified as the first parameter. The directory specified in the first parameter is not removed.
#define _POSIX_C_SOURCE 200809L
#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h>
#include <dirent.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <errno.h>
int main(int argc, char *argv[])
{
DIR *dirp;
int arg, retval;
if (argc < 3 || !strcmp(argv[1], "-h") || !strcmp(argv[1], "--help")) {
fprintf(stderr, "\n");
fprintf(stderr, "Usage: %s [ -h | --help ]\n", argv[0]);
fprintf(stderr, " %s BASE-DIRECTORY ITEM-TO-REMOVE ...\n", argv[0]);
fprintf(stderr, "\n");
return EXIT_FAILURE;
}
dirp = opendir(argv[1]);
if (!dirp) {
fprintf(stderr, "%s: %s.\n", argv[1], strerror(errno));
return EXIT_FAILURE;
}
retval = EXIT_SUCCESS;
for (arg = 2; arg < argc; arg++) {
if (unlinkat(dirfd(dirp), argv[arg], AT_REMOVEDIR)) {
fprintf(stderr, "%s: %s.\n", argv[arg], strerror(errno));
retval = EXIT_FAILURE;
}
}
closedir(dirp);
return retval;
}