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

       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 -1.

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 open.

              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.1‐2017, dirent.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic
       form from IEEE Std 1003.1-2017, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The
       Open Group Base Specifications Issue 7, 2018 Edition, Copyright
       (C) 2018 by the Institute of Electrical and Electronics
       Engineers, Inc and The Open Group.  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               2017                     ALPHASORT(3P)

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