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NAME
ftw, nftw - file tree walk
SYNOPSIS
#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
DESCRIPTION
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()
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.
RETURN VALUE
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().
VERSIONS
nftw() is available under glibc since version 2.1.
ATTRIBUTES
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 │
└──────────┴───────────────┴─────────────┘
CONFORMING TO
POSIX.1-2001, POSIX.1-2008, SVr4, SUSv1. POSIX.1-2008 marks ftw() as obsolete.
NOTES
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().
BUGS
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).
EXAMPLE
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 <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);
}
SEE ALSO
stat(2), fts(3), readdir(3)
COLOPHON
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