FTW(3)                    Linux Programmer's Manual                   FTW(3)

NAME         top

       ftw, nftw - file tree walk

SYNOPSIS         top

       #include <ftw.h>

       int ftw(const char *dirpath,
               int (*fn) (const char *fpath, const struct stat *sb,
                          int typeflag),
               int nopenfd);

       #define _XOPEN_SOURCE 500   /* See feature_test_macros(7) */
       #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);

DESCRIPTION         top

       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 (preorder traversal).

       To avoid using up all of the calling process's file descriptors,
       nopenfd specifies the maximum number of directories that ftw() will
       hold open simultaneously.  When the search depth exceeds this, ftw()
       will become slower because directories have to be closed and
       reopened.  ftw() uses at most one file descriptor for each level in
       the directory tree.

       For each entry found in the tree, ftw() calls fn() with three
       arguments: fpath, sb, and typeflag.  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 ftw(),
       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.  typeflag is an integer that has one of the following values:

       FTW_F  fpath is a regular file.

       FTW_D  fpath is a directory.

              fpath is a directory which can't be read.

       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).

              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 typeflag.

       To stop the tree walk, fn() returns a nonzero value; this value will
       become the return value of ftw().  As long as fn() returns 0, 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 ftw() 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 function nftw() is the same as ftw(), except that it has one
       additional argument, flags, and calls fn() with one more argument,

       This flags argument is formed by ORing zero or more of the following

       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:

                     Instructs nftw() to continue normally.

                     If fn() returns this value, then siblings of the
                     current entry will be skipped, and processing continues
                     in the parent.

                     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.

                     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>.

              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.)

              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.)

              If set, stay within the same filesystem (i.e., do not cross
              mount points).

              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.

       For each entry in the directory tree, nftw() calls fn() with four
       arguments.  fpath and sb are as for ftw().  typeflag may receive any
       of the same values as with ftw(), or any of the following values:

       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_SL fpath is a symbolic link, and FTW_PHYS was set in flags.

              fpath is a symbolic link pointing to a nonexistent file.
              (This occurs only if FTW_PHYS is not set.)

       The fourth argument that 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 fpath.  level is the depth of fpath in the
       directory tree, relative to the root of the tree (dirpath, which has
       depth 0).

RETURN VALUE         top

       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().

VERSIONS         top

       nftw() is available under glibc since version 2.1.

CONFORMING TO         top

       POSIX.1-2001, SVr4, SUSv1.  POSIX.1-2008 marks ftw() as obsolete.

NOTES         top

       POSIX.1-2001 note that the results are unspecified if fn does not
       preserve the current working directory.

       The function nftw() and the use of FTW_SL with ftw() were introduced
       in SUSv1.

       On some systems 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.  For predictable control, use nftw().

       FTW_F is returned for all objects (files, symbolic links, FIFOs,
       etc.)  that can be stat'ed but are not a directory.

       FTW_ACTIONRETVAL is glibc-specific.

EXAMPLE         top

       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 <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) ?   "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 */

       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) {

SEE ALSO         top

       stat(2), fts(3), readdir(3)

COLOPHON         top

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Linux                            2014-12-31                           FTW(3)