FTW(3P)                                             POSIX Programmer's Manual                                            FTW(3P)



PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (con-
       sult the corresponding Linux manual page for details of Linux behavior), or the  interface  may  not  be  implemented  on
       Linux.

NAME
       ftw - traverse (walk) a file tree

SYNOPSIS
       #include <ftw.h>

       int ftw(const char *path, int (*fn)(const char *,
              const struct stat *ptr, int flag), int ndirs);


DESCRIPTION
       The  ftw()  function  shall recursively descend the directory hierarchy rooted in path. For each object in the hierarchy,
       ftw() shall call the function pointed to by fn, passing it a pointer to a null-terminated character string containing the
       name of the object, a pointer to a stat structure containing information about the object, and an integer.  Possible val-
       ues of the integer, defined in the <ftw.h> header, are:

       FTW_D  For a directory.

       FTW_DNR
              For a directory that cannot be read.

       FTW_F  For a file.

       FTW_SL For a symbolic link (but see also FTW_NS below).

       FTW_NS For an object other than a symbolic link on which stat() could not successfully be executed. If the  object  is  a
              symbolic  link  and  stat()  failed,  it is unspecified whether ftw() passes FTW_SL or FTW_NS to the user-supplied
              function.


       If the integer is FTW_DNR, descendants of that directory shall not be processed. If  the  integer  is  FTW_NS,  the  stat
       structure contains undefined values. An example of an object that would cause FTW_NS to be passed to the function pointed
       to by fn would be a file in a directory with read but without execute (search) permission.

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

       The ftw() function shall use at most one file descriptor for each level in the tree.

       The argument ndirs should be in the range [1, {OPEN_MAX}].

       The tree traversal shall continue until either the tree is exhausted, an invocation of fn returns a  non-zero  value,  or
       some error, other than [EACCES], is detected within ftw().

       The ndirs argument shall specify the maximum number of directory streams or file descriptors or both available for use by
       ftw() while traversing the tree. When ftw() returns it shall close any directory streams and file descriptors it uses not
       counting any opened by the application-supplied fn function.

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

       The  ftw()  function need not be reentrant. A function that is not required to be reentrant is not required to be thread-
       safe.

RETURN VALUE
       If the tree is exhausted, ftw() shall return 0. If the function pointed to by fn returns a non-zero  value,  ftw()  shall
       stop  its  tree  traversal  and  return whatever value was returned by the function pointed to by fn. If ftw() detects an
       error, it shall return -1 and set errno to indicate the error.

       If ftw() encounters an error other than [EACCES] (see FTW_DNR and FTW_NS above), it shall return  -1  and  set  errno  to
       indicate  the  error. The external variable errno may 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() function shall fail if:

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

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

       ENAMETOOLONG
              The length of the path argument exceeds {PATH_MAX} or a pathname 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 may fail if:

       EINVAL The value of the ndirs argument is invalid.

       ELOOP  More than {SYMLOOP_MAX} symbolic links were encountered during resolution of the path argument.

       ENAMETOOLONG
              Pathname resolution of a symbolic link produced an intermediate result whose length exceeds {PATH_MAX}.


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

       The following sections are informative.

EXAMPLES
   Walking a Directory Structure
       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);
              }

APPLICATION USAGE
       The ftw() function may allocate dynamic storage during its operation.  If  ftw()  is  forcibly  terminated,  such  as  by
       longjmp()  or siglongjmp() being executed by the function pointed to by fn or an interrupt routine, ftw() 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.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       longjmp(),  lstat(),  malloc(),   nftw(),   opendir(),   siglongjmp(),   stat(),   the   Base   Definitions   volume   of
       IEEE Std 1003.1-2001, <ftw.h>, <sys/stat.h>

COPYRIGHT
       Portions  of  this  text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for
       Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6,  Copy-
       right (C) 2001-2003 by the Institute of Electrical and Electronics Engineers, Inc and The Open Group. In the event of any
       discrepancy between this version and the original IEEE and The Open Group Standard, the original IEEE and The Open  Group
       Standard   is   the   referee   document.   The   original   Standard   can   be   obtained  online  at  http://www.open-
       group.org/unix/online.html .



IEEE/The Open Group                                           2003                                                       FTW(3P)