ftw(3) - Linux manual page (original) (raw)

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_**);**

   **[[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 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)](../man2/stat.2.html) 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 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)](../man2/stat.2.html) 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)](../man2/stat.2.html).  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_ argument passed to _fn_() contains information
          returned by performing [lstat(2)](../man2/lstat.2.html) 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)](../man3/malloc.3.html) 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)](../man3/longjmp.3.html) 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:

          **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
                 (_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.

          **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
          including _any_ header files) in order to obtain the
          definition of **FTW_ACTIONRETVAL** from _<ftw.h>_.

   **FTW_CHDIR**
          If set, do a [chdir(2)](../man2/chdir.2.html) 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_.)

   **FTW_DEPTH**
          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.)

   **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 (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
   **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 top

   For an explanation of the terms used in this section, see
   [attributes(7)](../man7/attributes.7.html).
   ┌─────────────────────────────────┬───────────────┬─────────────┐
   │ **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)](../man2/stat.2.html) 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

   POSIX.1-2008.

HISTORY top

   **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 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)](../man2/lstat.2.html) 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" : "???",
              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 top

   [stat(2)](../man2/stat.2.html), [fts(3)](../man3/fts.3.html), [readdir(3)](../man3/readdir.3.html)

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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)