posix man page for alphasort

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

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

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
", 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 sig-
       longjmp() 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.1-2008, <dirent.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technol-
       ogy -- 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 Stan-
       dard is the referee document. The original Standard can be obtained online at http://www.unix.org/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						       2013							     ALPHASORT(3P)