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man: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
     selected.
     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
     selected.   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
     attributes(7).
     allbox;  lbw26  lb  lb  l l l.  Interface Attribute Value T{ scandir(),
     scandirat() T}   Thread safety  MT-Safe T{  alphasort(),  versionsort()
     T}   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 4.16 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)

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