ftw(3) Library Functions Manual ftw(3)
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 direc-
tory dirpath, and calls fn() once for each entry in the tree. By de-
fault, 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 al-
ways 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 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). 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 argu-
ment 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 be-
come 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 fol-
lowing flags:
FTW_ACTIONRETVAL (since glibc 2.3.3)
If this glibc-specific flag is set, then nftw() handles the re-
turn 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 (type-
flag 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 in-
cluding 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 ac-
tion 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 di-
rectory itself after handling the contents of the directory and
its subdirectories. (By default, each directory is handled be-
fore 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 (possi-
bly) 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 pre-
serve 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 eventu-
ally 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)
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