Reference

ftw(3)

traverse (walk) a file tree

NAME

ftw, nftw – traverse (walk) a file tree

SYNOPSIS

#include <ftw.h>

int

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

int

nftw(const char *path, int (*fn)(const char *, const struct stat *ptr, int flag, struct FTW *), int depth, int flags);

DESCRIPTION

These functions are provided for compatibility with legacy code. New code should use the fts(3) functions.

The ftw() and nftw() functions traverse (walk) the directory hierarchy rooted in path. For each object in the hierarchy, these functions call the function pointed to by fn. The ftw() function passes this function a pointer to a NUL-terminated string containing the name of the object, a pointer to a stat structure corresponding to the object, and an integer flag. The nftw() function passes the aforementioned arguments plus a pointer to a FTW structure as defined by ⟨ftw.h⟩ (shown below):

struct FTW {
    int base;	/* offset of basename into pathname */
    int level;	/* directory depth relative to starting point */
};

Possible values for the flag passed to fn are:

FTW_F

A regular file.

FTW_D

A directory being visited in pre-order.

FTW_DNR

A directory which cannot be read. The directory will not be descended into.

FTW_DP

A directory being visited in post-order (nftw() only).

FTW_NS

A file for which no stat(2) information was available. The contents of the stat structure are undefined.

FTW_SL

A symbolic link.

FTW_SLN

A symbolic link with a non-existent target (nftw() only).

The ftw() function traverses the tree in pre-order. That is, it processes the directory before the directory's contents.

The depth argument specifies the maximum number of file descriptors to keep open while traversing the tree. It has no effect in this implementation.

The nftw() function has an additional flags argument with the following possible values:

FTW_PHYS

Physical walk, don't follow symbolic links.

FTW_MOUNT

The walk will not cross a mount point.

FTW_DEPTH

Process directories in post-order. Contents of a directory are visited before the directory itself. By default, nftw() traverses the tree in pre-order.

FTW_CHDIR

Change to a directory before reading it. By default, nftw() will change its starting directory. The current working directory will be restored to its original value before nftw() returns.

RETURN VALUES

If the tree was traversed successfully, the ftw() and nftw() functions return 0. If the function pointed to by fn returns a non-zero value, ftw() and nftw() will stop processing the tree and return the value from fn. Both functions return -1 if an error is detected.

ERRORS

The ftw() and nftw() functions may fail and set errno for any of the errors specified for the library functions close(2), open(2), stat(2), malloc(3), opendir(3) and readdir(3). If the FTW_CHDIR flag is set, the nftw() function may fail and set errno for any of the errors specified for chdir(2). In addition, either function may fail and set errno as follows:

[EINVAL]

The depth argument is less than 1 or greater than OPEN_MAX.

LEGACY ERRORS

The ftw() and nftw() functions are far more tolerant of symlink cycles and are lax in reporting errors while accessing the initial path. When nftw() is passed FTW_MOUNT, it will pass the mount point to the callback function.

SEE ALSO

chdir(2), close(2), open(2), stat(2), fts(3), malloc(3), opendir(3), readdir(3), compat(5)

STANDARDS

The ftw() and nftw() functions conform to IEEE Std 1003.1-2001 (“POSIX.1”) Version 3 of the Single UNIX Specification (“SUSv3”).

HISTORY

Prior to MacOS X 10.4 ftw did not follow symlinks.

BUGS

The depth argument is currently ignored.

History