ftw(3C)
NAME
ftw, lftw, nftw − walk a file tree
SYNOPSIS
#include <ftw.h>
int ftw (const char ∗path, int (∗fn) (const char ∗, const struct
stat ∗, int), int depth);
int lftw (const char ∗path, int (∗fn) (const char ∗, const struct
stat ∗, int), int depth);
int nftw (const char ∗path, int (∗fn) (const char ∗, const struct
stat ∗, int, struct FTW∗), int depth, int flags);
DESCRIPTION
ftw recursively descends the directory hierarchy rooted in path. For each object in the hierarchy, ftw calls the user-defined function fn, passing it a pointer to a null-terminated character string containing the name of the object, a pointer to a stat structure (see stat(2)) containing information about the object, and an integer. 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_DNR
The object is a directory that cannot be read. Descendants of the directory will not be processed.
FTW_NS stat failed on the object because of lack of appropriate permission or the object is a symbolic link that points to a non-existent file. The stat buffer passed to fn is undefined.
ftw visits a directory before visiting any of its descendants.
The tree traversal continues until the tree is exhausted, an invocation of fn returns a nonzero value, or some 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 whatever value was returned by fn. If ftw detects an error other than EACCES, it returns −1, and sets the error type in errno.
lftw is identical to ftw except lstat(2) is invoked instead of stat(2). Using lstat only effects symbolic links. Therefore, if an object in the hierarchy is a symbolic link, then the stat structure passed to the function indicates that the object is a symbolic link and does not provide information about the object that the link points to, as ftw would do. A second side effect is that a symbolic link to a directory is treated as a symbolic link (and is not traversed). See NOTES, below.
The function nftw is similar to ftw except that it takes an additional argument, flags. The flags field is used to specify:
FTW_PHYS
Physical walk, does not follow symbolic links. Otherwise, nftw will follow links but will not walk down any path that crosses itself.
FTW_MOUNT
The walk will not cross a mount point.
FTW_DEPTH
All subdirectories will be visited before the directory itself.
FTW_CHDIR
The walk will change to each directory before reading it.
The function nftw calls fn with four arguments at each file and directory. The first argument is the pathname of the object, the second is a pointer to the stat buffer, the third is an integer giving additional information, and the fourth is a struct FTW that contains the following members:
int base;
int level;
base is the offset into the pathname of the base name of the object. level indicates the depth relative to the rest of the walk, where the root level is zero.
The values of the third argument are 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.
FTW_SLN
The object is a symbolic link that points to a non-existent file.
FTW_DNR
The object is a directory that cannot be read. fn will not be called for any of its descendants.
FTW_NS stat failed on the object because of lack of appropriate permission. The stat buffer passed to fn is undefined. stat failure other than lack of appropriate permission (EACCES) is considered an error and nftw will return −1.
These functions use one file descriptor for each level in the tree. The depth argument limits the number of file descriptors so used. If depth is zero 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. The functions will run faster if depth is at least as large as the number of levels in the tree. When these functions return, they close any file descriptors they have opened; they do not close any file descriptors that may have been opened by fn. All file descriptors used by these functions have the FD_CLOEXEC flag set.
SEE ALSO
NOTES
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 lftw use malloc(3C) to allocate dynamic storage during its operation. If they are forcibly terminated, such as by longjmp being executed by fn or an interrupt routine, they will not have a chance to free that storage, so it will remain 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.
lftw is a non-standard interface that is provided only for compatibility with previous CX/UX releases. Its use is discouraged; use nftw with the FTW_PHYS flag instead.
CX/UX Programmer’s Reference Manual