NFTW(3P) POSIX Programmer's Manual NFTW(3P)PROLOG
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.
NAMEnftw — walk a file tree
SYNOPSIS
#include <ftw.h>
int nftw(const char *path, int (*fn)(const char *,
const struct stat *, int, struct FTW *), int fd_limit, int flags);
DESCRIPTION
The nftw() function shall recursively descend the directory hierarchy
rooted in path. The nftw() function has a similar effect to ftw()
except that it takes an additional argument flags, which is a bitwise-
inclusive OR of zero or more of the following flags:
FTW_CHDIR If set, nftw() shall change the current working directory
to each directory as it reports files in that directory. If
clear, nftw() shall not change the current working direc‐
tory.
FTW_DEPTH If set, nftw() shall report all files in a directory before
reporting the directory itself. If clear, nftw() shall
report any directory before reporting the files in that
directory.
FTW_MOUNT If set, nftw() shall only report files in the same file
system as path. If clear, nftw() shall report all files
encountered during the walk.
FTW_PHYS If set, nftw() shall perform a physical walk and shall not
follow symbolic links.
If FTW_PHYS is clear and FTW_DEPTH is set, nftw() shall follow links
instead of reporting them, but shall not report any directory that
would be a descendant of itself. If FTW_PHYS is clear and FTW_DEPTH is
clear, nftw() shall follow links instead of reporting them, but shall
not report the contents of any directory that would be a descendant of
itself.
At each file it encounters, nftw() shall call the user-supplied func‐
tion fn with four arguments:
* The first argument is the pathname of the object.
* The second argument is a pointer to the stat buffer containing
information on the object, filled in as if fstatat(), stat(), or
lstat() had been called to retrieve the information.
* The third argument is an integer giving additional information. Its
value is one of the following:
FTW_D The object is a directory.
FTW_DNR The object is a directory that cannot be read. The fn
function shall not be called for any of its descendants.
FTW_DP The object is a directory and subdirectories have been
visited. (This condition shall only occur if the
FTW_DEPTH flag is included in flags.)
FTW_F The object is a non-directory file.
FTW_NS The stat() function failed on the object because of lack
of appropriate permission. The stat buffer passed to fn
is undefined. Failure of stat() for any other reason is
considered an error and nftw() shall return −1.
FTW_SL The object is a symbolic link. (This condition shall only
occur if the FTW_PHYS flag is included in flags.)
FTW_SLN The object is a symbolic link that does not name an
existing file. (This condition shall only occur if the
FTW_PHYS flag is not included in flags.)
* The fourth argument is a pointer to an FTW structure. The value of
base is the offset of the object's filename in the pathname passed
as the first argument to fn. The value of level indicates depth
relative to the root of the walk, where the root level is 0.
The results are unspecified if the application-supplied fn function
does not preserve the current working directory.
The argument fd_limit sets the maximum number of file descriptors that
shall be used by nftw() while traversing the file tree. At most one
file descriptor shall be used for each directory level.
The nftw() function need not be thread-safe.
RETURN VALUE
The nftw() function shall continue until the first of the following
conditions occurs:
* An invocation of fn shall return a non-zero value, in which case
nftw() shall return that value.
* The nftw() function detects an error other than [EACCES] (see
FTW_DNR and FTW_NS above), in which case nftw() shall return −1 and
set errno to indicate the error.
* The tree is exhausted, in which case nftw() shall return 0.
ERRORS
The nftw() function shall fail if:
EACCES Search permission is denied for any component of path or read
permission is denied for path, or fn returns −1 and does not
reset errno.
ELOOP A loop exists in symbolic links encountered during resolution of
the path argument.
ENAMETOOLONG
The length of a component of a pathname is longer than
{NAME_MAX}.
ENOENT A component of path does not name an existing file or path is an
empty string.
ENOTDIR
A component of path names an existing file that is neither a
directory nor a symbolic link to a directory.
EOVERFLOW
A field in the stat structure cannot be represented correctly in
the current programming environment for one or more files found
in the file hierarchy.
The nftw() function may fail if:
ELOOP More than {SYMLOOP_MAX} symbolic links were encountered during
resolution of the path argument.
EMFILE All file descriptors available to the process are currently
open.
ENAMETOOLONG
The length of a pathname exceeds {PATH_MAX}, or pathname resolu‐
tion 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.
In addition, errno may be set if the function pointed to by fn causes
errno to be set.
The following sections are informative.
EXAMPLES
The following program traverses the directory tree under the path named
in its first command-line argument, or under the current directory if
no argument is supplied. It displays various information about each
file. The second command-line argument can be used to specify charac‐
ters that control the value assigned to the flags argument when calling
nftw().
#include <ftw.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdint.h>
static int
display_info(const char *fpath, const struct stat *sb,
int tflag, struct FTW *ftwbuf)
{
printf("%-3s %2d %7jd %-40s %d %s\n",
(tflag == FTW_D) ? "d" : (tflag == FTW_DNR) ? "dnr" :
(tflag == FTW_DP) ? "dp" : (tflag == FTW_F) ?
(S_ISBLK(sb->st_mode) ? "f b" :
S_ISCHR(sb->st_mode) ? "f c" :
S_ISFIFO(sb->st_mode) ? "f p" :
S_ISREG(sb->st_mode) ? "f r" :
S_ISSOCK(sb->st_mode) ? "f s" : "f ?") :
(tflag == FTW_NS) ? "ns" : (tflag == FTW_SL) ? "sl" :
(tflag == FTW_SLN) ? "sln" : "?",
ftwbuf->level, (intmax_t) sb->st_size,
fpath, ftwbuf->base, fpath + ftwbuf->base);
return 0; /* To tell nftw() to continue */
}
int
main(int argc, char *argv[])
{
int flags = 0;
if (argc > 2 && strchr(argv[2], 'd') != NULL)
flags |= FTW_DEPTH;
if (argc > 2 && strchr(argv[2], 'p') != NULL)
flags |= FTW_PHYS;
if (nftw((argc < 2) ? "." : argv[1], display_info, 20, flags) == -1)
{
perror("nftw");
exit(EXIT_FAILURE);
}
exit(EXIT_SUCCESS);
}
APPLICATION USAGE
The nftw() function may allocate dynamic storage during its operation.
If nftw() is forcibly terminated, such as by longjmp() or siglongjmp()
being executed by the function pointed to by fn or an interrupt rou‐
tine, nftw() 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, and arrange to have the function
pointed to by fn return a non-zero value at its next invocation.
RATIONALE
None.
FUTURE DIRECTIONS
None.
SEE ALSOfdopendir(), fstatat(), readdir()
The Base Definitions volume of POSIX.1‐2008, <ftw.h>
COPYRIGHT
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 Electri‐
cal 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.ker‐
nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 NFTW(3P)
