DESCRIPTION

nftw() walks through the directory tree that is located under the directory dirpath, and calls fn() once for each entry in the tree. By default, directories are handled before the files and subdirectories they contain (preorder traversal).

To avoid using up all of the calling process_zsingle_quotesz_s file descriptors, nopenfd specifies the maximum number of directories that nftw() will hold open simultaneously. When the search depth exceeds this, nftw() will become slower because directories have to be closed and reopened. nftw() uses at most one file descriptor for each level in the directory tree.

For each entry found in the tree, nftw() calls fn() with four arguments: fpath, sb, typeflag, and ftwbuf. fpath is the pathname of the entry, and is expressed either as a pathname relative to the calling process_zsingle_quotesz_s current working directory at the time of the call to nftw(), if dirpath was expressed as a relative pathname, or as an absolute pathname, if dirpath was expressed as an absolute pathname. sb is a pointer to the stat structure returned by a call to stat(2) for fpath.

The typeflag argument passed to fn() is an integer that has one of the following values:

The fourth argument (ftwbuf) that nftw() supplies when calling fn() is a pointer to a structure of type FTW:

base is the offset of the filename (i.e., basename component) in the pathname given in fpath. level is the depth of fpath in the directory tree, relative to the root of the tree (dirpath, which has depth 0).

To stop the tree walk, fn() returns a nonzero value; this value will become the return value of nftw(). As long as fn() returns 0, nftw() will continue either until it has traversed the entire tree, in which case it will return zero, or until it encounters an error (such as a malloc(3) failure), in which case it will return −1.

Because nftw() uses dynamic data structures, the only safe way to exit out of a tree walk is to return a nonzero value from fn(). To allow a signal to terminate the walk without causing a memory leak, have the handler set a global flag that is checked by fn(). Don_zsingle_quotesz_t use longjmp(3) unless the program is going to terminate.

The flags argument of nftw() is formed by ORing zero or more of the following flags:

RETURN VALUE

These functions return 0 on success, and −1 if an error occurs.

If fn() returns nonzero, then the tree walk is terminated and the value returned by fn() is returned as the result of ftw() or nftw().

If nftw() is called with the FTW_ACTIONRETVAL flag, then the only nonzero value that should be used by fn() to terminate the tree walk is FTW_STOP, and that value is returned as the result of nftw().

VERSIONS

nftw() is available under glibc since version 2.1.

ATTRIBUTES

For an explanation of the terms used in this section, see attributes(7).

CONFORMING TO

POSIX.1-2001, POSIX.1-2008, SVr4, SUSv1. POSIX.1-2008 marks ftw() as obsolete.

NOTES

POSIX.1-2008 notes that the results are unspecified if fn does not preserve the current working directory.

The function nftw() and the use of FTW_SL with ftw() were introduced in SUSv1.

In some implementations (e.g., glibc), 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. If fpath is a symbolic link and stat(2) failed, POSIX.1-2008 states that it is undefined whether FTW_NS or FTW_SL is passed in typeflag. For predictable results, use nftw().

BUGS

In the specification of nftw(), POSIX.1 notes that when FTW_NS is passed as the typeflag argument of fn(), then the contents of the buffer pointed to by the sb argument are undefined. The standard makes no such statement for the case where FTW_SLN is passed in typeflag, with the implication that the contents of the buffer pointed to by sb are defined. And indeed this is the case on most implementations: the buffer pointed to by sb contains the results produced by applying lstat(2) to the symbolic link. In early glibc, the behavior was the same. However, since glibc 2.4, the contents of the buffer pointed to by sb are undefined when FTW_SLN is passed in typeflag. This change appears to be an unintended regression, but it is not (yet) clear if the behavior will be restored to that provided in the original glibc implementation (and on other implementations).

EXAMPLE

The following program traverses the directory tree under the path named in its first command-line argument, or under the current directory if no argument is supplied. It displays various information about each file. The second command-line argument can be used to specify characters that control the value assigned to the flags argument when calling nftw().

#define _XOPEN_SOURCE 500
#include <ftw.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdint.h>

static int
display_info(const char *fpath, const struct stat *sb,
             int tflag, struct FTW *ftwbuf)
{
    printf(%−3s %2d ,
            (tflag == FTW_D) ?   d   : (tflag == FTW_DNR) ? dnr :
            (tflag == FTW_DP) ?  dp  : (tflag == FTW_F) ?   f :
            (tflag == FTW_NS) ?  ns  : (tflag == FTW_SL) ?  sl :
            (tflag == FTW_SLN) ? sln : ???,
            ftwbuf−>level);

    if (tflag == FTW_NS)
        printf(−−−−−−−);
    else
        printf(%7jd, (intmax_t) sb−>st_size);

    printf(   %−40s %d %s
,
            fpath, ftwbuf−>base, fpath + ftwbuf−>base);

    return 0;           /* To tell nftw() to continue */
}

int
main(int argc, char *argv[])
{
    int flags = 0;

    if (argc > 2 && strchr(argv[2], _zsingle_quotesz_d_zsingle_quotesz_) != NULL)
        flags |= FTW_DEPTH;
    if (argc > 2 && strchr(argv[2], _zsingle_quotesz_p_zsingle_quotesz_) != NULL)
        flags |= FTW_PHYS;

    if (nftw((argc < 2) ? . : argv[1], display_info, 20, flags)
            == −1) {
        perror(nftw);
        exit(EXIT_FAILURE);
    }

    exit(EXIT_SUCCESS);
}

SEE ALSO

stat(2), fts(3), readdir(3)