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FTW(3) Linux Programmer's Manual FTW(3)
NAME
ftw, nftw - file tree walk
SYNOPSIS
#include <ftw.h>
int ftw(const char *dirpath,
int (*fn) (const char *fpath, const struct stat *sb,
int typeflag),
int nopenfd);
#define _XOPEN_SOURCE 500 /* See feature_test_macros(7) */
#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);
DESCRIPTION
ftw() walks through the directory tree that is located under the direc-
tory 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 ftw() will
hold open simultaneously. When the search depth exceeds this, ftw()
will become slower because directories have to be closed and reopened.
ftw() uses at most one file descriptor for each level in the directory
tree.
For each entry found in the tree, ftw() calls fn() with three argu-
ments: fpath, sb, and typeflag. 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 ftw(), 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. typeflag 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_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 permis-
sion 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).
If fpath is a symbolic link and stat(2) failed, POSIX.1-2001
states that it is undefined whether FTW_NS or FTW_SL (see below)
is passed in typeflag.
To stop the tree walk, fn() returns a nonzero value; this value will
become the return value of ftw(). As long as fn() returns 0, ftw()
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 ftw() 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.
nftw()
The function nftw() is the same as ftw(), except that it has one addi-
tional argument, flags, and calls fn() with one more argument, ftwbuf.
This flags argument 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 argu-
ments 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 con-
tents. This is useful if the program needs to perform some
action in the directory in which fpath resides.
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.
For each entry in the directory tree, nftw() calls fn() with four argu-
ments. fpath and sb are as for ftw(). typeflag may receive any of the
same values as with ftw(), or any of the following values:
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_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.)
The fourth argument that nftw() supplies when calling fn() is a struc-
ture 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).
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().
CONFORMING TO
POSIX.1-2001, SVr4, SUSv1. POSIX.1-2008 marks ftw() as obsolete.
NOTES
POSIX.1-2001 note that the results are unspecified if fn does not pre-
serve the current working directory.
The function nftw() and the use of FTW_SL with ftw() were introduced in
SUSv1.
On some systems 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. For predictable control, use nftw().
Under Linux, libc4 and libc5 and glibc 2.0.6 will use FTW_F for all
objects (files, symbolic links, FIFOs, etc.) that can be stat'ed but
are not a directory.
The function nftw() is available since glibc 2.1.
FTW_ACTIONRETVAL is glibc-specific.
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 charac-
ters 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 %7jd %-40s %d %s\n",
(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, (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);
}
SEE ALSO
stat(2), fts(3), readdir(3)
COLOPHON
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Linux 2014-01-11 FTW(3)
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