nftw(), nftw64()

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

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 nftw() function is faster if depth 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.

These functions are in libc.a, but not in libc.so (in order to save space).

Description:

The nftw() and nftw64() functions recursively descend the directory hierarchy identified by path. The nftw64() function is a 64-bit version of nftw(). 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. The stat buffer passed to fn() is undefined.
    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 a 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 behaviour 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 do not 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 XSI; nftw64() is Large-file support

Safety:  
Cancellation point Yes
Interrupt handler No
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.

Last modified: 2013-12-23

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