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



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

NAME
       alphasort, scandir -- scan a directory

SYNOPSIS
       #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
       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
       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 -1.

ERRORS
       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.

       ENAMETOOLONG
              The length of a component of a pathname is longer than
              {NAME_MAX}.

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

       ENOMEM Insufficient storage space is available.

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

       EOVERFLOW
              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.

       ENAMETOOLONG
              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
       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)
                   perror("scandir");
               else {
                   for (i = 0; i < n; i++) {
                       printf("%s\n", namelist[i]->d_name);
                       free(namelist[i]);
                       }
                   }
               free(namelist);
           ...

APPLICATION USAGE
       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
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       qsort(), strcoll()

       The Base Definitions volume of POSIX.1-2017, <dirent.h>

COPYRIGHT
       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 http://www.opengroup.org/unix/online.html .

       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
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .



IEEE/The Open Group                  2017                         ALPHASORT(3)
