NAME
ftw, nftw - file tree walk SYNOPSIS
#include
int ftw(const char *dirpath, int (*fn) (const char *fpath, const struct stat *sb, int typeflag), int nopenfd); #define XOPENSOURCE 500 /* See featuretestmacros(7) */
#include
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 direc‐ tory 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 argu‐ ments: 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: FTWF fpath is a regular file. FTWD fpath is a directory. FTWDNR fpath is a directory which can't be read. FTWNS 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 FTWNS or FTWSL (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. nftw() The function nftw() is the same as ftw(), except that it has one addi‐ tional argument, flags, and calls fn() with one more argument, ftwbuf. This flags argument is formed by ORing zero or more of the following flags: FTWACTIONRETVAL (since glibc 2.3.3)
If this glibc-specific flag is set, then nftw() handles the return value from fn() differently. fn() should return one of the following values: FTWCONTINUE Instructs nftw() to continue normally. FTWSKIPSIBLINGS If fn() returns this value, then siblings of the current entry will be skipped, and processing continues in the parent. FTWSKIPSUBTREE If fn() is called with an entry that is a directory (typeflag is FTWD), this return value will prevent objects within that directory from being passed as argu‐ ments to fn(). nftw() continues processing with the next sibling of the directory. FTWSTOP Causes nftw() to return immediately with the return value FTWSTOP. Other return values could be associated with new actions in the future; fn() should not return values other than those listed above. The feature test macro GNUSOURCE must be defined (before including any header files) in order to obtain the definition of FTWACTIONRETVAL from
. FTWCHDIR If set, do a chdir(2) to each directory before handling its con‐ tents. This is useful if the program needs to perform some action in the directory in which fpath resides. FTWDEPTH If set, do a post-order traversal, that is, call fn() for the directory itself after handling the contents of the directory and its subdirectories. (By default, each directory is handled before its contents.) FTWMOUNT If set, stay within the same file system (i.e., do not cross mount points). FTWPHYS If set, do not follow symbolic links. (This is what you want.) If not set, symbolic links are followed, but no file is reported twice. If FTWPHYS is not set, but FTWDEPTH is set, then the function fn() is never called for a directory that would be a descendant of itself. For each entry in the directory tree, nftw() calls fn() with four argu‐ ments. fpath and sb are as for ftw(). typeflag may receive any of the same values as with ftw(), or any of the following values: FTWDP fpath is a directory, and FTWDEPTH was specified in flags. All of the files and subdirectories within fpath have been pro‐ cessed. FTWSL fpath is a symbolic link, and FTWPHYS was set in flags. FTWSLN fpath is a symbolic link pointing to a nonexistent file. (This occurs only if FTWPHYS is not set.) The fourth argument that nftw() supplies when calling fn() is a struc‐ ture of type FTW: struct FTW { int base; int level; }; 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). 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 FTWACTIONRETVAL flag, then the only nonzero value that should be used by fn() to terminate the tree walk is FTWSTOP, 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 pre‐ serve the current working directory. The function nftw() and the use of FTWSL with ftw() were introduced in SUSv1. On some systems ftw() will never use FTWSL, on other systems FTWSL occurs only for symbolic links that do not point to an existing file, and again on other systems ftw() will use FTWSL for each symbolic link. For predictable control, use nftw(). Under Linux, libc4 and libc5 and glibc 2.0.6 will use FTWF 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.
FTWACTIONRETVAL 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 charac‐ ters that control the value assigned to the flags argument when calling nftw().
#define XOPENSOURCE 500
#include
#include
#include
#include
#include
static int displayinfo(const char *fpath, const struct stat *sb, int tflag, struct FTW *ftwbuf) { printf("%-3s %2d %7jd %-40s %d %s\n", (tflag == FTWD) ? "d" : (tflag == FTWDNR) ? "dnr" : (tflag == FTWDP) ? "dp" : (tflag == FTWF) ? "f" : (tflag == FTWNS) ? "ns" : (tflag == FTWSL) ? "sl" : (tflag == FTWSLN) ? "sln" : "???",
ftwbuf->level, (intmaxt) sb->stsize,
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 |= FTWDEPTH; if (argc > 2 && strchr(argv[2], 'p') != NULL) flags |= FTWPHYS; if (nftw((argc < 2) ? "." : argv[1], displayinfo, 20, flags)
== -1) { perror("nftw"); exit(EXITFAILURE); } exit(EXITSUCCESS); } SEE ALSO stat(2), fts(3), readdir(3) COLOPHON
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Linux 2010-09-20 FTW(3)