ftw()

Walk a file tree

Synopsis:

#include <ftw.h>

int ftw( const char *path, 
         int (*fn)( const char *fname,
                    struct stat *sbuf,
                    int flags),
         int depth );

Library:

libc

Description:

The ftw() function recursively descends the directory hierarchy identified by path. For each object in the hierarchy, ftw() calls the user-defined function fn(), passing it a pointer to a NULL-terminated character string containing the name of the object, a pointer to a stat structure (see stat()) containing information about the object, and an integer. Possible values of the integer, defined in the <ftw.h> header, are:

FTW_F

The object is a file.

FTW_D

The object is a directory.

FTW_DNR

The object is a directory that can't be read. Descendents of the directory aren't processed.

FTW_NS

The stat() failed on the object because the permissions weren't appropriate, or the object is a symbolic link that points to a nonexistent file. The stat buffer passed to fn() is undefined.

The ftw() function visits a directory before visiting any of its descendents.

The tree traversal continues until the tree is exhausted, an invocation of fn() returns a nonzero value, or some error is detected within ftw() (such as an I/O error). If the tree is exhausted, ftw() returns zero. If fn() returns a nonzero value, ftw() stops its tree traversal and returns whatever value was returned by fn().

The ftw() function uses one file descriptor for each level in the tree. The depth argument limits the number of file descriptors so used. If depth is zero or negative, the effect is the same as if it were 1. The depth must not be greater than the number of file descriptors currently available for use. The ftw() function is faster if depth is at least as large as the number of levels in the tree. When ftw() returns, it closes any file descriptors it opened; it doesn't close any file descriptors that may have been opened by fn().

Returns:

0

Success.

-1

An error (other than EACCESS) occurred; errno is set.

Classification:

Standard Unix

Caveats:

Because ftw() is recursive, it might terminate with a memory fault when applied to very deep file structures.

This function uses malloc() to allocate dynamic storage during its operation. If ftw() is forcibly terminated, for example if longjmp() is executed by fn() or an interrupt routine, ftw() doesn't 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 fn() return a nonzero value at its next invocation.

See also:

longjmp(), malloc(), stat()