FTW(3) Linux Programmers Manual FTW(3)
NAME
ftw, nftw - file tree walk
SYNOPSIS
#include
int ftw(const char *dirpath,
int (*fn) (const char *fpath, const struct stat *sb,
int typeflag),
int nopenfd);
#define _XOPEN_SOURCE 500
#include
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 (pre-order traversal).
To avoid using up all of the calling processs 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
relative to dirpath. 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 cant be read.
FTW_NS The stat(2) call failed on fpath, which is not a symbolic link.
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 non-zero 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 non-zero 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(). Dont 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 in order to
obtain the definition of FTW_ACTIONRETVAL from .
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 file system (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. All
of the files and subdirectories within fpath have been pro
cessed.
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 non-zero, 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 non-
zero 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.
NOTES
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 stated 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().
#define _XOPEN_SOURCE 500
#include
#include
#include
#include
#include
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), feature_test_macros(7)
COLOPHON
This page is part of release 3.05 of the Linux man-pages project. A
description of the project, and information about reporting bugs, can
be found at http://www.kernel.org/doc/man-pages/.
Linux 2007-07-26 FTW(3)
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