alphasort(3p) — Linux manual page


ALPHASORT(3P)             POSIX Programmer's Manual            ALPHASORT(3P)

PROLOG         top

       This manual page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the
       corresponding Linux manual page for details of Linux behavior), or
       the interface may not be implemented on Linux.

NAME         top

       alphasort, scandir — scan a directory

SYNOPSIS         top

       #include <dirent.h>

       int alphasort(const struct dirent **d1, const struct dirent **d2);
       int scandir(const char *dir, struct dirent ***namelist,
           int (*sel)(const struct dirent *),
           int (*compar)(const struct dirent **, const struct dirent **));

DESCRIPTION         top

       The alphasort() function can be used as the comparison function for
       the scandir() function to sort the directory entries, d1 and d2, into
       alphabetical order. Sorting happens as if by calling the strcoll()
       function on the d_name element of the dirent structures passed as the
       two parameters. If the strcoll() function fails, the return value of
       alphasort() is unspecified.

       The alphasort() function shall not change the setting of errno if
       successful. Since no return value is reserved to indicate an error,
       an application wishing to check for error situations should set errno
       to 0, then call alphasort(), then check errno.

       The scandir() function shall scan the directory dir, calling the
       function referenced by sel on each directory entry. Entries for which
       the function referenced by sel returns non-zero shall be stored in
       strings allocated as if by a call to malloc(), and sorted as if by a
       call to qsort() with the comparison function compar, except that
       compar need not provide total ordering. The strings are collected in
       array namelist which shall be allocated as if by a call to malloc().
       If sel is a null pointer, all entries shall be selected.  If the
       comparison function compar does not provide total ordering, the order
       in which the directory entries are stored is unspecified.

RETURN VALUE         top

       Upon successful completion, the alphasort() function shall return an
       integer greater than, equal to, or less than 0, according to whether
       the name of the directory entry pointed to by d1 is lexically greater
       than, equal to, or less than the directory pointed to by d2 when both
       are interpreted as appropriate to the current locale. There is no
       return value reserved to indicate an error.

       Upon successful completion, the scandir() function shall return the
       number of entries in the array and a pointer to the array through the
       parameter namelist.  Otherwise, the scandir() function shall return

ERRORS         top

       The scandir() function shall fail if:

       EACCES Search permission is denied for the component of the path
              prefix of dir or read permission is denied for dir.

       ELOOP  A loop exists in symbolic links encountered during resolution
              of the dir argument.

              The length of a component of a pathname is longer than

       ENOENT A component of dir does not name an existing directory or dir
              is an empty string.

       ENOMEM Insufficient storage space is available.

              A component of dir names an existing file that is neither a
              directory nor a symbolic link to a directory.

              One of the values to be returned or passed to a callback
              function cannot be represented correctly.

       The scandir() function may fail if:

       ELOOP  More than {SYMLOOP_MAX} symbolic links were encountered during
              resolution of the dir argument.

       EMFILE All file descriptors available to the process are currently

              The length of a pathname exceeds {PATH_MAX}, or pathname
              resolution of a symbolic link produced an intermediate result
              with a length that exceeds {PATH_MAX}.

       ENFILE Too many files are currently open in the system.

       The following sections are informative.

EXAMPLES         top

       An example to print the files in the current directory:

           #include <dirent.h>
           #include <stdio.h>
           #include <stdlib.h>
           struct dirent **namelist;
           int i,n;

               n = scandir(".", &namelist, 0, alphasort);
               if (n < 0)
               else {
                   for (i = 0; i < n; i++) {
                       printf("%s\n", namelist[i]->d_name);


       If dir contains filenames that do not form character strings, or
       which contain characters outside the domain of the collating sequence
       of the current locale, the alphasort() function need not provide a
       total ordering. This condition is not possible if all filenames
       within the directory consist only of characters from the portable
       filename character set.

       The scandir() function may allocate dynamic storage during its
       operation. If scandir() is forcibly terminated, such as by longjmp()
       or siglongjmp() being executed by the function pointed to by sel or
       compar, or by an interrupt routine, scandir() does not have a chance
       to free that storage, so it remains permanently allocated. A safe way
       to handle interrupts is to store the fact that an interrupt has
       occurred, then wait until scandir() returns to act on the interrupt.

       For functions that allocate memory as if by malloc(), the application
       should release such memory when it is no longer required by a call to
       free().  For scandir(), this is namelist (including all of the
       individual strings in namelist).

RATIONALE         top




SEE ALSO         top

       qsort(3p), strcoll(3p)

       The Base Definitions volume of POSIX.1‐2008, dirent.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The Open
       Group Base Specifications Issue 7, Copyright (C) 2013 by the
       Institute of Electrical and Electronics Engineers, Inc and The Open
       Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
       applied.) In the event of any discrepancy between this version and
       the original IEEE and The Open Group Standard, the original IEEE and
       The Open Group Standard is the referee document. The original
       Standard can be obtained online at .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the
       source files to man page format. To report such errors, see .

IEEE/The Open Group                 2013                       ALPHASORT(3P)

Pages that refer to this page: dirent.h(0p)qsort(3p)scandir(3p)strcoll(3p)strcoll_l(3p)