FTW(3) Linux Programmer's Manual FTW(3)
ftw, nftw - file tree walk
int ftw(const char *dir, int (*fn)(const char *file, const struct stat
*sb, int flag), int depth);
int nftw(const char *dir, int (*fn)(const char *file, const struct stat
*sb, int flag, struct FTW *s), int depth, int flags);
ftw() walks through the directory tree starting from the indicated
directory dir. For each found entry in the tree, it calls fn() with
the full pathname of the entry, a pointer to the stat(2) structure for
the entry and an int flag, which value will be one of the following:
FTW_F Item is a normal file
FTW_D Item is a directory
Item is a directory which can't be read
FTW_SL Item is a symbolic link
FTW_NS The stat failed on the item which is not a symbolic link
If the item is a symbolic link and stat failed, XPG4v2 states that it
is undefined whether FTW_NS or FTW_SL is used.
ftw() recursively calls itself for traversing found directories, han-
dling a directory before its files or subdirectories. To avoid using
up all a program's file descriptors, the depth specifies the number of
simultaneous open directories. When the depth is exceeded, ftw() will
become slower because directories have to be closed and reopened. ftw()
uses at most one file descriptor for each level in the file hierarchy.
To stop the tree walk, fn() returns a non-zero value; this value will
become the return value of ftw(). Otherwise, ftw() will continue until
it has traversed the entire tree, in which case it will return zero, or
until it hits an error other than EACCES (such as a malloc(3) failure),
in which case it will return -1.
Because ftw() uses dynamic data structures, the only safe way to exit
out of a tree walk is to return a non-zero value. To handle inter-
rupts, for example, mark that the interrupt occurred and return a non-
zero value¿don't use longjmp(3) unless the program is going to termi-
The function nftw() does precisely the same as ftw(), except that it
has one additional argument flags (and calls the supplied function with
one more argument). This flags argument is an OR of zero or more of
the following flags:
If set, do a chdir() to each directory before handling its con-
If set, do a depth-first search, that is, call the function for
the directory itself only after handling the contents of the
directory and its subdirectories.
If set, stay within the same file system.
If set, do not follow symbolic links. (This is what you want.)
If not set, symbolic links are followed, but no file is reported
If FTW_PHYS is not set, but FTW_DEPTH is set, then the function fn() is
never called for a directory that would be a descendant of itself.
The function fn() is called with four arguments: the pathname of the
reported entry, a pointer to a struct stat for this entry, an integer
describing its type, and a pointer to a struct FTW. The type will be
one of the following: FTW_F, FTW_D, FTW_DNR, FTW_SL, FTW_NS (with mean-
ing as above; FTW_SL occurs only with FTW_PHYS set) or
FTW_DP Item is a directory and all its descendants have been handled
already. (This occurs only with FTW_DEPTH set.)
Item is a symbolic link pointing to a nonexisting file. (This
occurs only with FTW_PHYS unset.)
The struct FTW pointed at by the fourth argument to fn() has at least
the fields base, the offset of the item's filename in the pathname
given as first argument of fn(), and level, the depth of the item rela-
tive to the starting point (which has depth 0).
The function nftw() and the use of FTW_SL with ftw() were introduced in
On some systems ftw() will never use FTW_SL, on other systems FTW_SL
occurs only for symbolic links that do not point to an existing file,
and again on other systems ftw() will use FTW_SL for each symbolic
link. For predictable control, use nftw().
Under Linux, libc4 and libc5 and glibc 2.0.6 will use FTW_F for all
objects (files, symbolic links, fifos, etc) that can be stat'ed but are
not a directory. The function nftw() is available since glibc 2.1.
AES, SVID2, SVID3, XPG2, XPG3, XPG4, XPG4v2.
Linux 1999-06-25 FTW(3)