scandir, scandirat, alphasort, versionsort - scan a directory for matching entries

#include <dirent.h>
int scandir(const char *restrict dirp,
 struct dirent ***restrict namelist,
 int (*filter)(const struct dirent *),
 int (*compar)(const struct dirent **,
 const struct dirent **));
int alphasort(const struct dirent **a, const struct dirent **b);
int versionsort(const struct dirent **a, const struct dirent **b);
#include <fcntl.h> /* Definition of AT_* constants */
#include <dirent.h>
int scandirat(int dirfd, const char *restrict dirp,
 struct dirent ***restrict namelist,
 int (*filter)(const struct dirent *),
 int (*compar)(const struct dirent **,
 const struct dirent **));

Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

    /* Since glibc 2.10: */ _POSIX_C_SOURCE >= 200809L
        || /* glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

    _GNU_SOURCE

    _GNU_SOURCE

The scandir() function scans the directory dirp, calling filter() on each directory entry. Entries for which filter() returns nonzero are stored in strings allocated via malloc(3), sorted using qsort(3) with the comparison function compar(), and collected in array namelist which is allocated via malloc(3). If filter is NULL, all entries are selected.

The alphasort() and versionsort() functions can be used as the comparison function compar(). The former sorts directory entries using strcoll(3), the latter using strverscmp(3) on the strings (*a)->d_name and (*b)->d_name.

scandirat()

The scandirat() function operates in exactly the same way as scandir(), except for the differences described here.

If the pathname given in dirp is relative, then it is interpreted relative to the directory referred to by the file descriptor dirfd (rather than relative to the current working directory of the calling process, as is done by scandir() for a relative pathname).

If dirp is relative and dirfd is the special value AT_FDCWD, then dirp is interpreted relative to the current working directory of the calling process (like scandir()).

If dirp is absolute, then dirfd is ignored.

See openat(2) for an explanation of the need for scandirat().

The scandir() function returns the number of directory entries selected. On error, -1 is returned, with errno set to indicate the error.

The alphasort() and versionsort() functions return an integer less than, equal to, or greater than zero if the first argument is considered to be respectively less than, equal to, or greater than the second.

The program below prints a list of the files in the current directory in reverse order.

Program source

#define _DEFAULT_SOURCE
#include <dirent.h>
#include <stdio.h>
#include <stdlib.h>
int
main(void)
{
    struct dirent **namelist;
    int n;
    n = scandir(".", &namelist, NULL, alphasort);
    if (n == -1) {
        perror("scandir");
        exit(EXIT_FAILURE);
    }
    while (n--) {
        printf("%s\n", namelist[n]->d_name);
        free(namelist[n]);
    }
    free(namelist);
    exit(EXIT_SUCCESS);
}

closedir(3), fnmatch(3), opendir(3), readdir(3), rewinddir(3), seekdir(3), strcmp(3), strcoll(3), strverscmp(3), telldir(3)