ftw(3p) — Linux manual page


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

PROLOG         top

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

NAME         top

       ftw — traverse (walk) a file tree

SYNOPSIS         top

       #include <ftw.h>

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

DESCRIPTION         top

       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, filled in as if stat() or lstat()
       had been called to retrieve the information. 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 non-directory 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)

       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 thread-safe.

RETURN VALUE         top

       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         top

       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.

              The length of a component of a pathname is longer than

       ENOENT A component of path does not name an existing file or path
              is an empty string.

              A component of path names an existing file that is neither
              a directory nor a symbolic link to a directory.

              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.

              The length of a pathname exceeds {PATH_MAX}, or pathname
              resolution of a symbolic link produced an intermediate
              result with a length that 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         top

   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);


       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.

       Applications should use the nftw() function instead of the
       obsolescent ftw() function.

RATIONALE         top



       The ftw() function may be removed in a future version.

SEE ALSO         top

       fdopendir(3p), fstatat(3p), longjmp(3p), nftw(3p), siglongjmp(3p)

       The Base Definitions volume of POSIX.1‐2017, ftw.h(0p),

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic
       form from IEEE Std 1003.1-2017, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The
       Open Group Base Specifications Issue 7, 2018 Edition, Copyright
       (C) 2018 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.opengroup.org/unix/online.html .

       Any typographical or formatting errors that appear in this page
       are most likely to have been introduced during the conversion of
       the source files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group               2017                           FTW(3P)

Pages that refer to this page: ftw.h(0p)