nftw(), nftw64()

QNX SDP8.0C Library ReferenceAPIDeveloper

Walk a file tree

Synopsis:

#include <ftw.h>

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

int nftw64( const char *path, 
            int (*fn)( const char *fname,
                       const struct stat64 *sbuf,
                       int flags, 
                       struct FTW *ftw),
            int fd_limit,
            int flags);

Arguments:

path

The path of the directory whose file tree you want to walk.

fn

A pointer to a function that you want to call for each file; see below.

fd_limit

The maximum number of file descriptors that nftw() can use. The nftw() function uses at most one file descriptor for each level in the tree.

If fd_limit is zero or negative, the effect is the same as if it were 1. The fd_limit value must not be greater than the number of file descriptors currently available for use. The nftw() function is faster if fd_limit is at least as large as the number of levels in the tree.

flags

The value of flags is constructed by the bitwise ORing of values from the following list, defined in the <ftw.h> header file.

FTW_CHDIR: If set, nftw() changes the current working directory to each directory as it reports files in that directory.
FTW_DEPTH: If set, nftw() reports all files in a directory before reporting the directory itself (otherwise the directory is reported before any file it contains).
FTW_MOUNT: If set, nftw() only reports files on the same filesystem as path.
FTW_PHYS: If set, nftw() performs a physical walk and doesn't follow any symbolic link.

Library:

libc

Use the -l c option to qcc to link against this library. This library is usually included automatically.

Description:

The nftw() and nftw64() functions recursively descend the directory hierarchy identified by path.

Note:

The nftw64() function is a large-file support version of nftw() provided for backwards compatibility. If you're using large-file support functions and data types, you should define _LARGEFILE64_SOURCE with a value of 1 to ensure they appear in the name space. For more information, see Classification in What's in a Function Description?.

For each object in the hierarchy, nftw() calls the user-defined function fn(), passing to 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
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_DP

The object is a directory, and its contents have been reported. See the FTW_DEPTH flag above.

FTW_NS

The stat() failed on the object because the permissions weren't appropriate. Don't assume that the stat buffer contains valid data.

FTW_SL

The object is a symbolic link. See the FTW_PHYS flag above.

FTW_SLN

The object is a symbolic link that does not name an existing file.
a pointer to an FTW structure, which contains the following fields:

base

The offset of the objects filename in the pathname passed as the first argument to fn().

level

The depth relative to the root of the walk (where the root is level 0).

quit

A flag that can be set to control the behavior of nftw() within the current directory. If assigned, it may be given the following values:

FTW_SKR

Skip the remainder of this directory

FTW_SKD

If the object is FTW_D, then don't enter into this directory.

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

When nftw() 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 EACCES) occurred (errno is set).

Classification:

nftw() is POSIX 1003.1; nftw64() is Large-file support


Safety:
Cancellation point	Yes
Signal handler	Yes
Thread	Yes

Caveats:

Because nftw() 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 nftw() is forcibly terminated, for example if longjmp() is executed by fn() or an interrupt routine, nftw() 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.

Page updated: December 04, 2024