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FTW(3P) POSIX Programmer's Manual FTW(3P)
This manual page is part of the POSIX Programmer's Manual. The Linux
implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
ftw — traverse (walk) a file tree
#include <ftw.h>
int ftw(const char *path, int (*fn)(const char *,
const struct stat *ptr, int flag), int ndirs);
The ftw() function shall recursively descend the directory hierarchy
rooted in path. For each object in the hierarchy, ftw() shall call
the function pointed to by 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,
filled in as if stat() or lstat() had been called to retrieve the
information. Possible values of the integer, defined in the <ftw.h>
header, are:
FTW_D For a directory.
FTW_DNR For a directory that cannot be read.
FTW_F For a non-directory file.
FTW_SL For a symbolic link (but see also FTW_NS below).
FTW_NS For an object other than a symbolic link on which stat()
could not successfully be executed. If the object is a
symbolic link and stat() failed, it is unspecified whether
ftw() passes FTW_SL or FTW_NS to the user-supplied
function.
If the integer is FTW_DNR, descendants of that directory shall not be
processed. If the integer is FTW_NS, the stat structure contains
undefined values. An example of an object that would cause FTW_NS to
be passed to the function pointed to by fn would be a file in a
directory with read but without execute (search) permission.
The ftw() function shall visit a directory before visiting any of its
descendants.
The ftw() function shall use at most one file descriptor for each
level in the tree.
The argument ndirs should be in the range [1,{OPEN_MAX}].
The tree traversal shall continue until either the tree is exhausted,
an invocation of fn returns a non-zero value, or some error, other
than [EACCES], is detected within ftw().
The ndirs argument shall specify the maximum number of directory
streams or file descriptors or both available for use by ftw() while
traversing the tree. When ftw() returns it shall close any directory
streams and file descriptors it uses not counting any opened by the
application-supplied fn function.
The results are unspecified if the application-supplied fn function
does not preserve the current working directory.
The ftw() function need not be thread-safe.
If the tree is exhausted, ftw() shall return 0. If the function
pointed to by fn returns a non-zero value, ftw() shall stop its tree
traversal and return whatever value was returned by the function
pointed to by fn. If ftw() detects an error, it shall return −1 and
set errno to indicate the error.
If ftw() encounters an error other than [EACCES] (see FTW_DNR and
FTW_NS above), it shall return −1 and set errno to indicate the
error. The external variable errno may contain any error value that
is possible when a directory is opened or when one of the stat
functions is executed on a directory or file.
The ftw() function shall fail if:
EACCES Search permission is denied for any component of path or read
permission is denied for path.
ELOOP A loop exists in symbolic links encountered during resolution
of the path argument.
ENAMETOOLONG
The length of a component of a pathname is longer than
{NAME_MAX}.
ENOENT A component of path does not name an existing file or path is
an empty string.
ENOTDIR
A component of path names an existing file that is neither a
directory nor a symbolic link to a directory.
EOVERFLOW
A field in the stat structure cannot be represented correctly
in the current programming environment for one or more files
found in the file hierarchy.
The ftw() function may fail if:
EINVAL The value of the ndirs argument is invalid.
ELOOP More than {SYMLOOP_MAX} symbolic links were encountered during
resolution of the path argument.
ENAMETOOLONG
The length of a pathname exceeds {PATH_MAX}, or pathname
resolution of a symbolic link produced an intermediate result
with a length that exceeds {PATH_MAX}.
In addition, if the function pointed to by fn encounters system
errors, errno may be set accordingly.
The following sections are informative.
Walking a Directory Structure
The following example walks the current directory structure, calling
the fn function for every directory entry, using at most 10 file
descriptors:
#include <ftw.h>
...
if (ftw(".", fn, 10) != 0) {
perror("ftw"); exit(2);
}
The ftw() function may allocate dynamic storage during its operation.
If ftw() is forcibly terminated, such as by longjmp() or siglongjmp()
being executed by the function pointed to by fn or an interrupt
routine, ftw() does not have a chance to free that storage, so it
remains permanently allocated. A safe way to handle interrupts is to
store the fact that an interrupt has occurred, and arrange to have
the function pointed to by fn return a non-zero value at its next
invocation.
Applications should use the nftw() function instead of the
obsolescent ftw() function.
None.
The ftw() function may be removed in a future version.
fdopendir(3p), fstatat(3p), longjmp(3p), nftw(3p), siglongjmp(3p)
The Base Definitions volume of POSIX.1‐2008, ftw.h(0p),
sys_stat.h(0p)
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1, 2013 Edition, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The Open
Group Base Specifications Issue 7, Copyright (C) 2013 by the
Institute of Electrical and Electronics Engineers, Inc and The Open
Group. (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1
applied.) In the event of any discrepancy between this version and
the original IEEE and The Open Group Standard, the original IEEE and
The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.unix.org/online.html .
Any typographical or formatting errors that appear in this page are
most likely to have been introduced during the conversion of the
source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 FTW(3P)
Pages that refer to this page: ftw.h(0p)