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       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.


       ftw — traverse (walk) a file tree


       #include <ftw.h>

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


       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) 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 thread-safe.


       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.


       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 {NAME_MAX}.

       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

       The following sections are informative.


   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.




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


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

       The Base Definitions volume of POSIX.1‐2008, <ftw.h>, <sys_stat.h>


       Portions of this text are reprinted and  reproduced  in  electronic  form  from  IEEE  Std
       1003.1,  2013  Edition,  Standard  for Information Technology -- Portable Operating System
       Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C) 2013  by  the
       Institute  of  Electrical  and  Electronics  Engineers,  Inc and The Open Group.  (This is
       POSIX.1-2008 with the  2013  Technical  Corrigendum  1  applied.)  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 .

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