ftw(3) — Linux manual page


ftw(3)                  Library Functions Manual                  ftw(3)

NAME         top

       ftw, nftw - file tree walk

LIBRARY         top

       Standard C library (libc, -lc)

SYNOPSIS         top

       #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);

       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

           _XOPEN_SOURCE >= 500

DESCRIPTION         top

       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.

              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

       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.)  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:

                     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.

       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

       •  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         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

       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

ATTRIBUTES         top

       For an explanation of the terms used in this section, see
       │ Interface                       Attribute     Value       │
       │ nftw()                          │ Thread safety │ MT-Safe cwd │
       │ ftw()                           │ Thread safety │ MT-Safe     │

VERSIONS         top

       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         top


HISTORY         top

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

       nftw() glibc 2.1.  POSIX.1-2001, SUSv1.

       FTW_SL POSIX.1-2001, SUSv1.

NOTES         top

       POSIX.1-2008 notes that the results are unspecified if fn does
       not preserve the current working directory.

BUGS         top

       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         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 <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" : "???",

           if (tflag == FTW_NS)
               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 */

       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 man-pages 6.9.1          2024-06-15                         ftw(3)

Pages that refer to this page: fts(3)readdir(3)attributes(7)