FTW
NAME
ftw, nftw - file tree walk
SYNOPSIS
#include <ftw.h>
I int ftw(const char * dirpath ,
R int (* fn ) (const char * fpath , const struct stat * sb ,
I int typeflag ),
I int nopenfd );
#define _XOPEN_SOURCE 500
#include <ftw.h>
I int nftw(const char * dirpath ,
I int (* fn ) (const char * fpath , const struct stat * sb ,
I int typeflag , struct FTW * ftwbuf ),
I int nopenfd , int flags );
DESCRIPTION
R ftw ()
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 (pre-order traversal).
To avoid using up all of the calling process's file descriptors,
nopenfd specifies the maximum number of directories that
R ftw ()
will hold open simultaneously.
When
the search depth exceeds this,
R ftw ()
will become slower because
directories have to be closed and reopened.
R ftw ()
uses at most
one file descriptor for each level in the directory tree.
For each entry found in the tree,
R ftw ()
calls
fn() with three arguments:
R fpath ,
R sb ,
and
R typeflag .
R fpath
is the pathname of the entry relative to
R dirpath .
R sb
is a pointer to the
R stat
structure returned by a call to
stat(2)
for
R fpath .
R typeflag
is an integer that has one of the following values:
FTW_F
fpath
is a normal 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
R 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
R typeflag .
To stop the tree walk,
fn() returns a non-zero value; this
value will become the return value of
R ftw ().
As long as
fn() returns 0,
R 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
R 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().
Don't use
longjmp(3)
unless the program is going to terminate.
nftw()
The function
R nftw ()
is the same as
R ftw (),
except that it has one additional argument,
flags,
and calls
fn() with one more argument,
ftwbuf.
This
flags argument is formed by ORing zero or more of the
following flags:
R FTW_ACTIONRETVAL (since glibc 2.3.3)
If this glibc-specific flag is set, then
R nftw ()
handles the return value from
R fn ()
differently.
R fn ()
should return one of the following values:
FTW_CONTINUE
Instructs
R 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().
R nftw ()
continues processing with the next sibling of the directory.
FTW_STOP
Causes
R 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.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.
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
R fn ()
is never called for a directory that would be a descendant of itself.
For each entry in the directory tree,
R nftw ()
calls
R fn ()
with four arguments.
fpath
and
sb
are as for
R ftw ().
typeflag
may receive any of the same values as with
R 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 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
R nftw ()
supplies when calling
fn()
is 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
R fpath .
R 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
R ftw ()
or
R nftw ().
If
R 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
R nftw ().
CONFORMING TO
POSIX.1-2001, SVr4, SUSv1.
NOTES
The function
R nftw ()
and the use of FTW_SL with
R ftw ()
were introduced in SUSv1.
On some systems
R 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
R ftw ()
will use FTW_SL for each symbolic link.
For predictable control, use
R 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
R 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 characters that
control the value assigned to the
flags
argument when calling
R nftw ().
#define _XOPEN_SOURCE 500
#include <ftw.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 %7lld %-40s %d %s\n",
(tflag == FTW_D) ? "d" : (tflag == FTW_DNR) ? "dnr" :
(tflag == FTW_DP) ? "dp" : (tflag == FTW_F) ? "f" :
(tflag == FTW_DP) ? "dp" : (tflag == FTW_SL) ? "sl" :
(tflag == FTW_SLN) ? "sln" : "???",
ftwbuf->level, (long long) 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;
nftw((argc < 2) ? "." : argv[1], display_info, 20, flags);
exit(EXIT_SUCCESS);
}
SEE ALSO
