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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 dif-
       fer (consult 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 values 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  inter-
       rupts  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, Stan-
       dard for Information Technology -- Portable Operating System Interface (POSIX), The Open Group Base  Specifica-
       tions  Issue  6,  Copyright (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 Stan-
       dard,  the  original  IEEE  and  The  Open Group Standard is the referee document. The original Standard can be
       obtained online at http://www.opengroup.org/unix/online.html .



IEEE/The Open Group                  2003                              FTW(3P)