ftw(3C)

NAME

ftw(), nftw(), nftw2() — walk a file tree executing a function

SYNOPSIS

#include <ftw.h> 

int ftw (const char *path, 
         int (*fn)(const char *obj_path, 
                   const struct stat *obj_stat, 
                   int obj_flags), 
         int depth); 

int nftw2(const char *path, 
          int (*fn)(const char *obj_path, 
                    const struct stat *obj_stat, 
                    int obj_flags, 
                    struct FTW obj_FTW), 
          int depth, 
          int flags); 

int nftw (const char *path, 
          int (*fn)(const char *obj_path, 
                    const struct stat *obj_stat, 
                    int obj_flags, 
                    struct FTW obj_FTW), 
          int depth, 
          int flags); 

UNIX95

int nftw (const char *path, 
          int (*fn)(const char *obj_path, 
                    const struct stat *obj_stat, 
                    int obj_flags, 
                    struct *FTW obj_FTW), 
          int depth, 
          int flags); 

DESCRIPTION

The ftw() function recursively descends the directory hierarchy rooted in path. For each object in the hierarchy, ftw() calls fn, passing it a pointer to a null-terminated character string containing the name of the object, a pointer to a stat structure containing information about the object (see lstat() in stat(2)), and an integer. The possible values of the integer, defined in the <ftw.h> header file, are:

FTW_F: The object is a file.
FTW_D: The object is a directory.
FTW_SL: The object is a symbolic link.
FTW_DNR: The object is a directory without read permission. fn will not be called for any of its descendants.
FTW_NS: lstat() failed on the object. The contents of the stat structure are undefined. If the lstat() failure is because the object is in a directory without search permission, fn is called and the walk continues. If lstat() fails for any other reason, ftw() does not call fn, it sets errno, and returns -1.

Tree traversal continues until the tree is exhausted, an invocation of fn returns a nonzero value, or an error is detected within ftw(), such as an I/O error. If the tree is exhausted, ftw() returns zero. If fn returns a nonzero value, ftw() stops its tree traversal and returns the same value as returned by fn. If ftw() detects an error, it returns -1 and sets the error type in errno (see errno(2)).

ftw() visits a directory before visiting any of its descendants.

ftw() and nftw() use one file descriptor for each level in the tree. The depth argument limits the number of file descriptors that can be used. If depth is 0 or negative, the effect is the same as if it were 1. depth must not be greater than the number of file descriptors currently available for use. For best performance, depth should be at least as large as the number of levels in the tree.

nftw() is similar to ftw() except that it takes the additional argument flags. The flags field is the inclusive OR of the following values, as defined in the <ftw.h> header file:

FTW_PHYS: nftw() does a physical walk. It does not follow symbolic links. nftw() follows hard links but does not walk down any path that crosses itself. If FTW_PHYS is not specified, nftw() follows symbolic and hard links but does not walk a path that crosses itself.
FTW_MOUNT: The walk does not cross a mount point. This means the walk does not visit any files that reside on a device other than the one where the walk started. It does not cross NFS mount points.
FTW_DEPTH: nftw() performs a depth-first search. This means that a directory's contents are visited before the directory itself is visited.
FTW_CHDIR: The walk does a chdir() (see chdir(2)) to each directory before reading it.
FTW_SERR: The walk normally terminates and returns -1 if lstat() fails for any reason. If FTW_SERR is specified and an lstat() failure is encountered, fn is called, and the walk continues.

nftw() calls fn with four arguments for each file and directory visited. The first argument is the path name of the file or directory, the second is a pointer to a stat structure (see lstat(2)) containing information about the object, and the third is an integer giving additional information as follows:

FTW_F: The object is a file.
FTW_D: The object is a directory.
FTW_DP: The object is a directory and subdirectories have been visited. This can be passed to fn only if FTW_DEPTH is specified.
FTW_SL: The object is a symbolic link. This can be passed to fn only if FTW_PHYS is specified.
FTW_SLN: The object is a symbolic link that does not point to an existing object. This can be passed to fn only if FTW_PHYS is not specified.
FTW_DNR: The object is a directory that cannot be read. fn is not called for any of its descendants.
FTW_NS: lstat() failed on the object. The contents of the stat structure passed to fn are undefined. If the lstat() failure occurred because the object is in a directory without search permission, errno is set, and nftw() returns -1 after calling fn. Note that this behavior differs from ftw(). If lstat() fails for any other reason, nftw() does not call fn, it sets errno, and returns -1. This behavior can be altered by specifying the FTW_SERR flag.

The fourth argument is different for the default environment and the UNIX95 environment. For the default environment, the fourth argument is a structure FTW. For the UNIX95 environment, the fourth argument is a pointer to a structure FTW (ie: *FTW ). FTW contains the following members:

int base; 
int level; 

The value of base is the offset from the first character in the path name to where the base name of the object starts; this path name is passed as the first argument to fn. The value of level indicates depth relative to the start of the walk, where the start level has a value of zero.

nftw2() is equivalent to nftw(). This function is provided for HP-UX compatibility in future releases.

APPLICATION USAGE

ftw(), nftw() and nftw2() are thread-safe. These interfaces are not async-cancel-safe. A cancellation point may occur when a thread is executing ftw(), nftw() or nftw2().

To use the UNIX95 prototype, the UNIX95 environment must be defined. This is done by defining the UNIX95 environment variable, passing the _XOPEN_UNIX_EXTENDED flag as a compiler option, and adding /usr/xpg4/bin to your path. This can be done as follows:

1.: export UNIX95=
2.: PATH=/usr/xpg4/bin:$PATH
3.: cc foo.c -D_XOPEN_SOURCE_EXTENDED

ERRORS

If ftw() or nftw() fails, it sets errno (see errno(2)) to one of the following values:

[EACCES]: If a component of the path prefix denies search permission, or if read permission is denied for path, fn returns -1 and does not reset errno.
[EINVAL]: The value of the depth argument is invalid.
[ENAMETOOLONG]: The length of the specified path name exceeds PATH_MAX bytes, or the length of a component of the path name exceeds NAME_MAX bytes while _POSIX_NO_TRUNC is in effect.
[ENOENT]: path points to the name of a file that does not exist, or points to an empty string.
[ENOTDIR]: A component of path is not a directory.
[EOVERFLOW]: One of the values in struct stat (st_size or st_blocks) is too large to store into the structure to be passed to the function pointed to by fn.

In addition, if the function pointed to by fn encounters system errors, errno may be set accordingly.

WARNINGS

Because these functions are recursive, it is possible for them to terminate with a memory fault when applied to very deep file structures.

ftw() and nftw() use malloc() to allocate dynamic storage during their operation (see malloc(3C)) If they are forcibly terminated (such as if longjmp() is executed by fn or an interrupt routine), the calling function will not have a chance to free that storage, causing it to remain allocated until the process terminates. 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.

The syntax for nftw() may be changed in a future release. (See nftw2() in the DESCRIPTION section).

AUTHOR

ftw(), nftw(), and nftw2() were developed by AT&T and HP.

STANDARDS CONFORMANCE

ftw(): AES, SVID2, SVID3, XPG2, XPG3, XPG4