ftw, nftw - file tree walk
#include <ftw.h>
int nftw(const char *dirpath,
int (*fn) (const char *fpath, const struct stat *sb,
int typeflag, struct FTW *ftwbuf),
int nopenfd, int flags);
#include <ftw.h>
int ftw(const char *dirpath,
int (*fn) (const char *fpath, const struct stat *sb,
int typeflag),
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.) On most implementations, in
this case the sb argument passed to fn() contains
information returned by performing lstat(2) on the symbolic link.
For the details on Linux, 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() 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().
nftw() is available under glibc since version 2.1.
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 |
POSIX.1-2001, POSIX.1-2008, SVr4, SUSv1. POSIX.1-2008 marks
ftw() as
obsolete.
POSIX.1-2008 notes that the results are unspecified if
fn does not
preserve the current working directory.
The function
nftw() and the use of
FTW_SL with
ftw() were
introduced in SUSv1.
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().
In the specification of
nftw(), POSIX.1 notes that when
FTW_NS is
passed as the
typeflag argument of
fn(), then the contents of
the buffer pointed to by the
sb argument are undefined. The standard
makes no such statement for the case where
FTW_SLN is passed in
typeflag, with the implication that the contents of the buffer pointed
to by
sb are defined. And indeed this is the case on most
implementations: the buffer pointed to by
sb contains the results
produced by applying
lstat(2) to the symbolic link. In early glibc, the
behavior was the same. However, since glibc 2.4, the contents of the buffer
pointed to by
sb are undefined when
FTW_SLN is passed in
typeflag. This change
appears to be an unintended regression,
but it is not (yet) clear if the behavior will be restored to that provided in
the original glibc implementation (and on other implementations).
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().
#define _XOPEN_SOURCE 500
#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 ",
(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)