NFTW
Section: POSIX Programmer's Manual (3P)
Updated: 2017
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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
nftw
--- 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 directory.
- 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 function
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 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.
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 characters
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 routine,
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 ALSO
fdopendir(),
fstatat(),
readdir()
The Base Definitions volume of POSIX.1-2017,
<ftw.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
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https://www.kernel.org/doc/man-pages/reporting_bugs.html .