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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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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.1‐2017, ftw.h(0p),
sys_stat.h(0p)
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 by the Institute of Electrical and Electronics Engineers,
Inc and The Open Group. 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.opengroup.org/unix/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 2017 FTW(3P)
Pages that refer to this page: ftw.h(0p)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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