Tribblix: manual page: ftw.3c

FTW(3C) Standard C Library Functions FTW(3C)

NAME

ftw, nftw - walk a file tree

SYNOPSIS

#include <ftw.h>

int ftw(const char *path, int (*fn) (const char *,
const struct stat *, int), int depth);

int nftw(const char *path, int (*fn) (const char *,
const struct stat *, int, struct FTW *), int depth,
int flags);

DESCRIPTION

The ftw() function recursively descends the directory hierarchy
rooted in path. For each object in the hierarchy, ftw() calls the
user-defined function fn, passing it a pointer to a null-terminated
character string containing the name of the object, a pointer to a
stat structure (see stat(2)) containing information about the object,
and an integer. Possible values of the integer, defined in the
<ftw.h> header, are:

FTW_F
The object is a file.

FTW_D
The object is a directory.

FTW_DNR
The object is a directory that cannot be read. Descendants
of the directory are not processed.

FTW_NS
The stat() function failed on the object because of lack
of appropriate permission or the object is a symbolic link
that points to a non-existent file. The stat buffer
passed to fn is undefined.

The ftw() function visits a directory before visiting any of its
descendants.

The tree traversal continues until the tree is exhausted, an
invocation of fn returns a non-zero value, or some error is detected
within ftw() (such as an I/O error). If the tree is exhausted, ftw()
returns 0. If fn returns a non-zero value, ftw() stops its tree
traversal and returns whatever value was returned by fn.

The nftw() function is similar to ftw() except that it takes the
additional argument flags, which is a bitwise-inclusive OR of zero or
more of the following flags:

FTW_CHDIR
If set, nftw() changes the current working directory to
each directory as it reports files in that directory. If
clear, nftw() does not change the current working
directory.

FTW_DEPTH
If set, nftw() reports all files in a directory before
reporting the directory itself. If clear, nftw() reports
any directory before reporting the files in that
directory.

FTW_MOUNT
If set, nftw() reports only files in the same file
system as path. If clear, nftw() reports all files
encountered during the walk.

FTW_PHYS
If set, nftw() performs a physical walk and does not
follow symbolic links.

If FTW_PHYS is clear and FTW_DEPTH is set, nftw() follows links
instead of reporting them, but does not report any directory that
would be a descendant of itself. If FTW_PHYS is clear and FTW_DEPTH
is clear, nftw() follows links instead of reporting them, but does
not report the contents of any directory that would be a descendant
of itself.

At each file it encounters, nftw() calls the user-supplied function
fn with four arguments:

o The first argument is the pathname of the object.

o The second argument is a pointer to the stat buffer
containing information on the object.

o The third argument is an integer giving additional
information. Its value is one of the following:

FTW_F
The object is a file.

FTW_D
The object is a directory.

FTW_DP
The object is a directory and subdirectories
have been visited. (This condition only occurs
if the FTW_DEPTH flag is included in flags.)

FTW_SL
The object is a symbolic link. (This condition
only occurs if the FTW_PHYS flag is included in
flags.)

FTW_SLN
The object is a symbolic link that points to a
non-existent file. (This condition only occurs
if the FTW_PHYS flag is not included in flags.)

FTW_DNR
The object is a directory that cannot be read.
The user-defined function fn will not be called
for any of its descendants.

FTW_NS
The stat() function failed on the object
because of lack of appropriate permission. The
stat buffer passed to fn is undefined. Failure
of stat() for any other reason is considered an
error and nftw() returns -1.

o The fourth argument is a pointer to an FTW structure that
contains the following members:

int base;
int level;

The base member is the offset of the object's filename in
the pathname passed as the first argument to fn(). The
value of level indicates the depth relative to the root of
the walk, where the root level is 0.

The results are unspecified if the application-supplied
fn() function does not preserve the current working
directory.

Both ftw() and nftw() use one file descriptor for each level in the
tree. The depth argument limits the number of file descriptors used.
If depth is zero or negative, the effect is the same as if it were 1.
It must not be greater than the number of file descriptors currently
available for use. The ftw() function runs faster if depth is at
least as large as the number of levels in the tree. Both ftw() and
nftw() are able to descend to arbitrary depths in a file hierarchy
and do not fail due to path length limitations unless either the
length of the path name pointed to by the path argument exceeds
{PATH_MAX} requirements, or for ftw(), the specified depth is less
than 2, or for nftw(), the specified depth is less than 2 and
FTW_CHDIR is not set. When ftw() and nftw() return, they close any
file descriptors they have opened; they do not close any file
descriptors that might have been opened by fn.

RETURN VALUES

If the tree is exhausted, ftw() and nftw() return 0. If the function
pointed to by fn returns a non-zero value, ftw() and nftw() stop
their tree traversal and return whatever value was returned by the
function pointed to by fn. If ftw() and nftw() detect an error, they
return -1 and set errno to indicate the error.

If ftw() and nftw() encounter an error other than EACCES (see FTW_DNR
and FTW_NS above), they return -1 and set errno to indicate the
error. The external variable errno can contain any error value that
is possible when a directory is opened or when one of the stat
functions is executed on a directory or file.

ERRORS

The ftw() and nftw() functions will fail if:

ELOOP
A loop exists in symbolic links encountered during
resolution of the path argument

ENAMETOOLONG
The length of the path name pointed to by the path
argument exceeds {PATH_MAX}, or a path name component
is longer than {NAME_MAX}.

ENOENT
A component of path does not name an existing file or
path is an empty string.

ENOTDIR
A component of path is not a directory.

EOVERFLOW
A field in the stat structure cannot be represented
correctly in the current programming environment for
one or more files found in the file hierarchy.

The ftw() function will fail if:

EACCES
Search permission is denied for any component of path
or read permission is denied for path.

ENAMETOOLONG
The ftw() function has descended to a path that
exceeds {PATH_MAX} and the depth argument specified
by the application is less than 2 and FTW_CHDIR is
not set.

The nftw() function will fail if:

EACCES
Search permission is denied for any component of path or
read permission is denied for path, or fn() returns -1 and
does not reset errno.

The nftw() and ftw() functions may fail if:

ELOOP
Too many symbolic links were encountered during
resolution of the path argument.

ENAMETOOLONG
Pathname resolution of a symbolic link in the path
name pointed to by the path argument produced an
intermediate result whose length exceeds {PATH_MAX}.

The ftw() function may fail if:

EINVAL
The value of the depth argument is invalid.

The nftw() function may fail if:

EMFILE
There are {OPEN_MAX} file descriptors currently open in the
calling process.

ENFILE
Too many files are currently open in the system.

If the function pointed to by fn encounters system errors, errno may
be set accordingly.

EXAMPLES

Example 1: Walk a directory structure using ftw().

The following example walks the current directory structure, calling
the fn() function for every directory entry, using at most 10 file
descriptors:

#include <ftw.h>
...
if (ftw(".", fn, 10) != 0) {
perror("ftw"); exit(2);
}

Example 2: Walk a directory structure using nftw().

The following example walks the /tmp directory and its
subdirectories, calling the nftw() function for every directory
entry, to a maximum of 5 levels deep.

#include <ftw.h>
...
int nftwfunc(const char *, const struct stat *, int, struct FTW *);
int nftwfunc(const char *filename, const struct stat *statptr,
int fileflags, struct FTW *pfwt)
{
return 0;
}
...
char *startpath = "/tmp";
int depth = 5;
int flags = FTW_CHDIR | FTW_DEPTH | FTW_MOUNT;
int ret;
ret = nftw(startpath, nftwfunc, depth, flags);

USAGE

Because ftw() and nftw() are recursive, they can terminate with a
memory fault when applied by a thread with a small stack to very deep
file structures.

The ftw() and nftw() functions allocate resources (memory, file
descriptors) during their operation. If ftw() they are forcibly
terminated, such as by longjmp(3C) being executed by fn or an
interrupt routine, they will not have a chance to free those
resources, so they remain permanently allocated. A safe way to handle
interrupts is to store the fact that an interrupt has occurred and
arrange to have fn return a non-zero value at its next invocation.

The ftw() and nftw() functions have transitional interfaces for
64-bit file offsets. See lf64(7).

The ftw() function is safe in multithreaded applications. The nftw()
function is safe in multithreaded applications when the FTW_CHDIR
flag is not set.

ATTRIBUTES