пройтись по файловому дереву (walk a file tree)
Пролог (Prolog)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
Имя (Name)
nftw — walk a file tree
Синопсис (Synopsis)
#include <ftw.h>
int nftw(const char *path, int (*fn)(const char *,
const struct stat *, int, struct FTW *), int fd_limit, int flags);
Описание (Description)
The nftw() function shall recursively descend the directory
hierarchy rooted in path. The nftw() function has a similar
effect to ftw() except that it takes an additional argument
flags, which is a bitwise-inclusive OR of zero or more of the
following flags:
FTW_CHDIR If set, nftw() shall change the current working
directory to each directory as it reports files in
that directory. If clear, nftw() shall not change the
current working directory.
FTW_DEPTH If set, nftw() shall report all files in a directory
before reporting the directory itself. If clear,
nftw() shall report any directory before reporting
the files in that directory.
FTW_MOUNT If set, nftw() shall only report files in the same
file system as path. If clear, nftw() shall report
all files encountered during the walk.
FTW_PHYS If set, nftw() shall perform a physical walk and
shall not follow symbolic links.
If FTW_PHYS is clear and FTW_DEPTH is set, nftw() shall follow
links instead of reporting them, but shall not report any
directory that would be a descendant of itself. If FTW_PHYS is
clear and FTW_DEPTH is clear, nftw() shall follow links instead
of reporting them, but shall not report the contents of any
directory that would be a descendant of itself.
At each file it encounters, nftw() shall call the user-supplied
function fn with four arguments:
* The first argument is the pathname of the object.
* The second argument is a pointer to the stat buffer
containing information on the object, filled in as if
fstatat(), stat(), or lstat() had been called to retrieve the
information.
* The third argument is an integer giving additional
information. Its value is one of the following:
FTW_D The object is a directory.
FTW_DNR The object is a directory that cannot be read. The
fn function shall not be called for any of its
descendants.
FTW_DP The object is a directory and subdirectories have
been visited. (This condition shall only occur if
the FTW_DEPTH flag is included in flags.)
FTW_F The object is a non-directory file.
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()
shall return -1.
FTW_SL The object is a symbolic link. (This condition
shall only occur if the FTW_PHYS flag is included
in flags.)
FTW_SLN The object is a symbolic link that does not name an
existing file. (This condition shall only occur if
the FTW_PHYS flag is not included in flags.)
* The fourth argument is a pointer to an FTW structure. The
value of base is the offset of the object's filename in the
pathname passed as the first argument to fn. The value of
level indicates 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.
The argument fd_limit sets the maximum number of file descriptors
that shall be used by nftw() while traversing the file tree. At
most one file descriptor shall be used for each directory level.
The nftw() function need not be thread-safe.
Возвращаемое значение (Return value)
The nftw() function shall continue until the first of the
following conditions occurs:
* An invocation of fn shall return a non-zero value, in which
case nftw() shall return that value.
* The nftw() function detects an error other than [EACCES] (see
FTW_DNR and FTW_NS above), in which case nftw() shall return
-1 and set errno to indicate the error.
* The tree is exhausted, in which case nftw() shall return 0.
Ошибки (Error)
The nftw() function shall 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.
ELOOP A loop exists in symbolic links encountered during
resolution of the path argument.
ENAMETOOLONG
The length of a component of a pathname 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 names an existing file that is neither
a directory nor a symbolic link to 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 nftw() function may fail if:
ELOOP More than {SYMLOOP_MAX} symbolic links were encountered
during resolution of the path argument.
EMFILE All file descriptors available to the process are
currently open.
ENAMETOOLONG
The length of a pathname exceeds {PATH_MAX}, or pathname
resolution of a symbolic link produced an intermediate
result with a length that exceeds {PATH_MAX}.
ENFILE Too many files are currently open in the system.
In addition, errno may be set if the function pointed to by fn
causes errno to be set.
The following sections are informative.
Примеры (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().
#include <ftw.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdint.h>
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) ?
(S_ISBLK(sb->st_mode) ? "f b" :
S_ISCHR(sb->st_mode) ? "f c" :
S_ISFIFO(sb->st_mode) ? "f p" :
S_ISREG(sb->st_mode) ? "f r" :
S_ISSOCK(sb->st_mode) ? "f s" : "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);
}
Использование в приложениях (Application usage)
The nftw() function may allocate dynamic storage during its
operation. If nftw() is forcibly terminated, such as by longjmp()
or siglongjmp() being executed by the function pointed to by fn
or an interrupt routine, nftw() does not have a chance to free
that storage, so it remains permanently allocated. A safe way to
handle interrupts is to store the fact that an interrupt has
occurred, and arrange to have the function pointed to by fn
return a non-zero value at its next invocation.
Обоснование (Rationale)
None.
Будущие направления (Future directions)
None.
Смотри также (See also)
fdopendir(3p), fstatat(3p), readdir(3p)
The Base Definitions volume of POSIX.1‐2017, ftw.h(0p)
