alphasort

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 *dirp, struct dirent ***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 *dirp, struct dirent ***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 versions <= 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 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  se-
       lected.

       The alphasort() and versionsort() functions can be used as the compari-
       son function compar().  The former sorts directory entries  using  str-
       coll(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 rela-
       tive 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  se-
       lected.  On error, -1 is returned, with errno set to indicate the cause
       of the error.

       The alphasort() and versionsort()  functions  return  an  integer  less
       than,  equal  to, or greater than zero if the first argument is consid-
       ered to be respectively less than, equal to, or greater than  the  sec-
       ond.

ERRORS
       ENOENT The path in dirp does not exist.

       ENOMEM Insufficient memory to complete the operation.

       ENOTDIR
              The path in dirp is not a directory.

       The following additional errors can occur for scandirat():

       EBADF  dirfd is not a valid file descriptor.

       ENOTDIR
              dirp is a relative path 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  at-
       tributes(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 str-
       cmp(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 argument 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.

EXAMPLE
       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)

COLOPHON
       This page is part of release 5.05 of the Linux  man-pages  project.   A
       description  of  the project, information about reporting bugs, and the
       latest    version    of    this    page,    can     be     found     at
       https://www.kernel.org/doc/man-pages/.

GNU                               2017-09-15                        SCANDIR(3)