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ALPHASORT(3P) POSIX Programmer's Manual ALPHASORT(3P)
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.
alphasort, scandir — scan a directory
#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 **));
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.
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.
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.
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);
...
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).
None.
None.
qsort(3p), strcoll(3p)
The Base Definitions volume of POSIX.1‐2008, dirent.h(0p)
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 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)
Pages that refer to this page: dirent.h(0p), qsort(3p), scandir(3p), strcoll(3p)