alphasort(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
   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().

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
   considered to be respectively less than, equal to, or greater than  the
   second.

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).

   
   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 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

   #define _DEFAULT_SOURCE
   /* print files in current directory in reverse order */
   #include <dirent.h>

   int
   main(void)
   {
       struct dirent **namelist;
       int n;

       n = scandir(".", &namelist, NULL, alphasort);
       if (n < 0)
           perror("scandir");
       else {
           while (n--) {
               printf("%s\n", namelist[n]->d_name);
               free(namelist[n]);
           }
           free(namelist);
       }
   }

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 4.09 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/.

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