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  #include <ftw.h> int ftw(const char *path, int (*fn) (const char *, const struct stat *, int), int depth);
  int nftw(const char *path, int (*fn) (const char *, const struct stat *, int, struct FTW *), int depth, int flags);:
  FTW_F
  FTW_D
  FTW_DNR
  FTW_NS, which is a bitwise-inclusive OR of zero or more of the following flags:
  FTW_CHDIR
  FTW_DEPTH
  FTW_MOUNT
  FTW_PHYS.
  At each file it encounters, nftw() calls the user-supplied function fn with four arguments:
  FTW_F
  FTW_D
  FTW_DP
  FTW_SL
  FTW_SLN
  FTW_DNR
  FTW_NS.:
  ELOOP
  ENAMETOOLONG
  ENOENT
  ENOTDIR
  EOVERFLOW
  The ftw() function will fail if:
  EACCES
  ENAMETOOLONG
  The nftw() function will fail if:
  EACCES
  The nftw() and ftw() functions may fail if:
  ELOOP
  ENAMETOOLONG
  The ftw() function may fail if:
  EINVAL
  The nftw() function may fail if:
  EMFILE
  ENFILE
  If the function pointed to by fn encounters system errors, errno may be set accordingly.
  Example 1 Walk a directory structure using ftw().
  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); }
  Example 2 Walk a directory structure using nftw().);), attributes(5), lf64(5), standards(5)