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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.
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 man page format. To report
such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .