SCANDIR(3)                                                              Linux Programmer's Manual                                                             SCANDIR(3)

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

SYNOPSIS
       #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)):

       scandir(), alphasort():
           /* Since glibc 2.10: */ _POSIX_C_SOURCE >= 200809L
               || /* Glibc <= 2.19: */ _BSD_SOURCE || _SVID_SOURCE

       versionsort():
           _GNU_SOURCE

       scandirat():
           _GNU_SOURCE

DESCRIPTION
       The  scandir() function scans the directory dirp, calling filter() on each directory entry.  Entries for which filter() returns nonzero are stored in strings al‐
       located 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 us‐
       ing 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().

RETURN VALUE
       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.

ERRORS
       EBADF  (scandirat()) dirp is relative but dirfd is neither AT_FDCWD nor a valid file descriptor.

       ENOENT The path in dirp does not exist.

       ENOMEM Insufficient memory to complete the operation.

       ENOTDIR
              The path in dirp is not a directory.

       ENOTDIR
              (scandirat()) dirp is a relative pathname and dirfd is a file descriptor referring to a file other than a directory.

VERSIONS
       versionsort() was added to glibc in version 2.1.

       scandirat() was added to glibc in version 2.15.

ATTRIBUTES
       For an explanation of the terms used in this section, see attributes(7).

       ┌───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┬───────────────┬────────────────┐
       │Interface                                                                                                                      │ Attribute     │ Value          │
       ├───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┼───────────────┼────────────────┤
       │scandir(), scandirat()                                                                                                         │ Thread safety │ MT-Safe        │
       ├───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┼───────────────┼────────────────┤
       │alphasort(), versionsort()                                                                                                     │ Thread safety │ MT-Safe locale │
       └───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────┴───────────────┴────────────────┘

CONFORMING TO
       alphasort(), scandir(): 4.3BSD, POSIX.1-2008.

       versionsort() and scandirat() are GNU extensions.

NOTES
       Since glibc 2.1, alphasort() calls strcoll(3); earlier it used strcmp(3).

       Before  glibc  2.10, the two arguments of alphasort() and versionsort() were typed as const void *.  When alphasort() was standardized in POSIX.1-2008, the argu‐
       ment type was specified as the type-safe const struct dirent **, and glibc 2.10 changed the definition of alphasort()  (and  the  nonstandard  versionsort())  to
       match the standard.

EXAMPLES
       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);
       }

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

GNU                                                                            2021-08-27                                                                     SCANDIR(3)