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NAME
ftw, nftw - file tree walk
LIBRARY
Standard C library (libc, -lc)
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);
[[deprecated]]
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.) In this case the sb argument passed to fn() contains information returned by performing
lstat(2) on the "dangling" symbolic link. (But 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().
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 │
└─────────────────────────────────────────────────────────────────────────┴───────────────┴─────────────┘
VERSIONS
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().
STANDARDS
POSIX.1-2008.
HISTORY
ftw() POSIX.1-2001, SVr4, SUSv1. POSIX.1-2008 marks it as obsolete.
nftw() glibc 2.1. POSIX.1-2001, SUSv1.
FTW_SL POSIX.1-2001, SUSv1.
NOTES
POSIX.1-2008 notes that the results are unspecified if fn does not preserve the current working
directory.
BUGS
According to POSIX.1-2008, when the typeflag argument passed to fn() contains FTW_SLN, the buffer pointed
to by sb should contain information about the dangling symbolic link (obtained by calling lstat(2) on the
link). Early glibc versions correctly followed the POSIX specification on this point. However, as a
result of a regression introduced in glibc 2.4, the contents of the buffer pointed to by sb were
undefined when FTW_SLN is passed in typeflag. (More precisely, the contents of the buffer were left
unchanged in this case.) This regression was eventually fixed in glibc 2.30, so that the glibc
implementation (once more) follows the POSIX specification.
EXAMPLES
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 <stdint.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 ",
(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)
Linux man-pages 6.7 2023-10-31 ftw(3)