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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ATTRIBUTES | VERSIONS | STANDARDS | HISTORY | NOTES | BUGS | EXAMPLES | SEE ALSO | COLOPHON |
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ftw(3) Library Functions Manual ftw(3)
ftw, nftw - file tree walk
Standard C library (libc, -lc)
#include <ftw.h>
int nftw(const char *dirpath,
typeof(int (const char *fpath, const struct stat *sb,
int typeflag, struct FTW *ftwbuf))
*fn,
int nopenfd, int flags);
[[deprecated]]
int ftw(const char *dirpath,
typeof(int (const char *fpath, const struct stat *sb,
int typeflag))
*fn,
int nopenfd);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
nftw():
_XOPEN_SOURCE >= 500
nftw() walks through the directory tree that is located under the
directory dirpath, and calls fn() once for each entry in the tree.
By default, directories are handled before the files and
subdirectories they contain (preorder traversal).
To avoid using up all of the calling process's file descriptors,
nopenfd specifies the maximum number of directories that nftw()
will hold open simultaneously. When the search depth exceeds
this, nftw() will become slower because directories have to be
closed and reopened. nftw() uses at most one file descriptor for
each level in the directory tree.
For each entry found in the tree, nftw() calls fn() with four
arguments: fpath, sb, typeflag, and ftwbuf. fpath is the pathname
of the entry, and is expressed either as a pathname relative to
the calling process's current working directory at the time of the
call to nftw(), if dirpath was expressed as a relative pathname,
or as an absolute pathname, if dirpath was expressed as an
absolute pathname. sb is a pointer to the stat structure returned
by a call to stat(2) for fpath.
The typeflag argument passed to fn() is an integer that has one of
the following values:
FTW_F fpath is a regular file.
FTW_D fpath is a directory.
FTW_DNR
fpath is a directory which can't be read.
FTW_DP fpath is a directory, and FTW_DEPTH was specified in flags.
(If FTW_DEPTH was not specified in flags, then directories
will always be visited with typeflag set to FTW_D.) All of
the files and subdirectories within fpath have been
processed.
FTW_NS The stat(2) call failed on fpath, which is not a symbolic
link. The probable cause for this is that the caller had
read permission on the parent directory, so that the
filename fpath could be seen, but did not have execute
permission, so that the file could not be reached for
stat(2). The contents of the buffer pointed to by sb are
undefined.
FTW_SL fpath is a symbolic link, and FTW_PHYS was set in flags.
FTW_SLN
fpath is a symbolic link pointing to a nonexistent file.
(This occurs only if FTW_PHYS is not set.) In this case
the sb argument passed to fn() contains information
returned by performing lstat(2) on the "dangling" symbolic
link. (But see BUGS.)
The fourth argument (ftwbuf) that nftw() supplies when calling
fn() is a pointer to a structure of type FTW:
struct FTW {
int base;
int level;
};
base is the offset of the filename (i.e., basename component) in
the pathname given in fpath. level is the depth of fpath in the
directory tree, relative to the root of the tree (dirpath, which
has depth 0).
To stop the tree walk, fn() returns a nonzero value; this value
will become the return value of nftw(). As long as fn() returns
0, nftw() will continue either until it has traversed the entire
tree, in which case it will return zero, or until it encounters an
error (such as a malloc(3) failure), in which case it will return
-1.
Because nftw() uses dynamic data structures, the only safe way to
exit out of a tree walk is to return a nonzero value from fn().
To allow a signal to terminate the walk without causing a memory
leak, have the handler set a global flag that is checked by fn().
Don't use longjmp(3) unless the program is going to terminate.
The flags argument of nftw() is formed by ORing zero or more of
the following flags:
FTW_ACTIONRETVAL (since glibc 2.3.3)
If this glibc-specific flag is set, then nftw() handles the
return value from fn() differently. fn() should return one
of the following values:
FTW_CONTINUE
Instructs nftw() to continue normally.
FTW_SKIP_SIBLINGS
If fn() returns this value, then siblings of the
current entry will be skipped, and processing
continues in the parent.
FTW_SKIP_SUBTREE
If fn() is called with an entry that is a directory
(typeflag is FTW_D), this return value will prevent
objects within that directory from being passed as
arguments to fn(). nftw() continues processing with
the next sibling of the directory.
FTW_STOP
Causes nftw() to return immediately with the return
value FTW_STOP.
Other return values could be associated with new actions in
the future; fn() should not return values other than those
listed above.
The feature test macro _GNU_SOURCE must be defined (before
including any header files) in order to obtain the
definition of FTW_ACTIONRETVAL from <ftw.h>.
FTW_CHDIR
If set, do a chdir(2) to each directory before handling its
contents. This is useful if the program needs to perform
some action in the directory in which fpath resides.
(Specifying this flag has no effect on the pathname that is
passed in the fpath argument of fn.)
FTW_DEPTH
If set, do a post-order traversal, that is, call fn() for
the directory itself after handling the contents of the
directory and its subdirectories. (By default, each
directory is handled before its contents.)
FTW_MOUNT
If set, stay within the same filesystem (i.e., do not cross
mount points).
FTW_PHYS
If set, do not follow symbolic links. (This is what you
want.) If not set, symbolic links are followed, but no
file is reported twice.
If FTW_PHYS is not set, but FTW_DEPTH is set, then the
function fn() is never called for a directory that would be
a descendant of itself.
ftw()
ftw() is an older function that offers a subset of the
functionality of nftw(). The notable differences are as follows:
• ftw() has no flags argument. It behaves the same as when
nftw() is called with flags specified as zero.
• The callback function, fn(), is not supplied with a fourth
argument.
• The range of values that is passed via the typeflag argument
supplied to fn() is smaller: just FTW_F, FTW_D, FTW_DNR,
FTW_NS, and (possibly) FTW_SL.
These functions return 0 on success, and -1 if an error occurs.
If fn() returns nonzero, then the tree walk is terminated and the
value returned by fn() is returned as the result of ftw() or
nftw().
If nftw() is called with the FTW_ACTIONRETVAL flag, then the only
nonzero value that should be used by fn() to terminate the tree
walk is FTW_STOP, and that value is returned as the result of
nftw().
For an explanation of the terms used in this section, see
attributes(7).
┌──────────────────────────────────┬───────────────┬─────────────┐
│ Interface │ Attribute │ Value │
├──────────────────────────────────┼───────────────┼─────────────┤
│ nftw() │ Thread safety │ MT-Safe cwd │
├──────────────────────────────────┼───────────────┼─────────────┤
│ ftw() │ Thread safety │ MT-Safe │
└──────────────────────────────────┴───────────────┴─────────────┘
In some implementations (e.g., glibc), ftw() will never use
FTW_SL; on other systems FTW_SL occurs only for symbolic links
that do not point to an existing file; and again on other systems
ftw() will use FTW_SL for each symbolic link. If fpath is a
symbolic link and stat(2) failed, POSIX.1-2008 states that it is
undefined whether FTW_NS or FTW_SL is passed in typeflag. For
predictable results, use nftw().
POSIX.1-2008.
ftw() POSIX.1-2001, SVr4, SUSv1. POSIX.1-2008 marks it as
obsolete.
nftw() glibc 2.1. POSIX.1-2001, SUSv1.
FTW_SL POSIX.1-2001, SUSv1.
POSIX.1-2008 notes that the results are unspecified if fn does not
preserve the current working directory.
According to POSIX.1-2008, when the typeflag argument passed to
fn() contains FTW_SLN, the buffer pointed to by sb should contain
information about the dangling symbolic link (obtained by calling
lstat(2) on the link). Early glibc versions correctly followed
the POSIX specification on this point. However, as a result of a
regression introduced in glibc 2.4, the contents of the buffer
pointed to by sb were undefined when FTW_SLN is passed in
typeflag. (More precisely, the contents of the buffer were left
unchanged in this case.) This regression was eventually fixed in
glibc 2.30, so that the glibc implementation (once more) follows
the POSIX specification.
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().
Program source
#define _XOPEN_SOURCE 500
#include <ftw.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
static int
display_info(const char *fpath, const struct stat *sb,
int tflag, struct FTW *ftwbuf)
{
printf("%-3s %2d ",
(tflag == FTW_D) ? "d" : (tflag == FTW_DNR) ? "dnr" :
(tflag == FTW_DP) ? "dp" : (tflag == FTW_F) ? "f" :
(tflag == FTW_NS) ? "ns" : (tflag == FTW_SL) ? "sl" :
(tflag == FTW_SLN) ? "sln" : "???",
ftwbuf->level);
if (tflag == FTW_NS)
printf("-------");
else
printf("%7jd", (intmax_t) sb->st_size);
printf(" %-40s %d %s\n",
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);
}
stat(2), fts(3), readdir(3)
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user-space interface documentation) project. Information about
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⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
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Linux man-pages 6.15 2025-05-17 ftw(3)
Pages that refer to this page: fts(3), readdir(3), attributes(7)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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