NAME¶

ftw, nftw - file tree walk

SYNOPSIS¶

#include <ftw.h>

int ftw(const char *dirpath,
        int (*fn) (const char *fpath, const struct stat *sb,
                   int typeflag),
        int nopenfd);

#define _XOPEN_SOURCE 500   /* See feature_test_macros(7) */
#include <ftw.h>

int nftw(const char *dirpath,
        int (*fn) (const char *fpath, const struct stat *sb,
                   int typeflag, struct FTW *ftwbuf),
        int nopenfd, int flags);

DESCRIPTION¶

ftw() 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's file descriptors, nopenfd specifies the maximum number of directories that ftw() will hold open simultaneously. When the search depth exceeds this, ftw() will become slower because directories have to be closed and reopened. ftw() uses at most one file descriptor for each level in the directory tree.

For each entry found in the tree, ftw() calls fn() with three arguments: fpath, sb, and typeflag. fpath is the pathname of the entry, and is expressed either as a pathname relative to the calling process's current working directory at the time of the call to ftw(), 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. typeflag is an integer that has one of the following values:

FTW_F

fpath is a regular file.

FTW_D

fpath is a directory.

FTW_DNR

fpath is a directory which can't be read.

FTW_NS

The stat(2) call failed on fpath, which is not a symbolic link.

If fpath is a symbolic link and stat(2) failed, POSIX.1-2001 states that it is undefined whether FTW_NS or FTW_SL (see below) is passed in typeflag.

To stop the tree walk, fn() returns a nonzero value; this value will become the return value of ftw(). As long as fn() returns 0, ftw() 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 ftw() 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't use longjmp(3) unless the program is going to terminate.

struct FTW {


    int base;


    int level;
};

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().

CONFORMING TO¶

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

NOTES¶

POSIX.1-2001 note 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.

On some systems 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. For predictable control, use nftw().

Under Linux, libc4 and libc5 and glibc 2.0.6 will use FTW_F for all objects (files, symbolic links, FIFOs, etc.) that can be stat'ed but are not a directory.

The function nftw() is available since glibc 2.1.

FTW_ACTIONRETVAL is glibc-specific.

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 %7jd   %-40s %d %s\n",


        (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, (intmax_t) sb->st_size,


        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], 'd') != NULL)


        flags |= FTW_DEPTH;


    if (argc > 2 && strchr(argv[2], 'p') != 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)

COLOPHON¶

This page is part of release 3.53 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.