Originální popis anglicky:
truncate, ftruncate - truncate a file to a specified length
Návod, kniha: Linux Programmer's Manual
int truncate(const char *path, off_t length);
int ftruncate(int fd, off_t length);
functions cause the regular file named
or referenced by fd
to be truncated to a size of
If the file previously was larger than this size, the extra data is lost. If the
file previously was shorter, it is extended, and the extended part reads as
The file pointer is not changed.
If the size changed, then the ctime and mtime fields for the file are updated,
and suid and sgid mode bits may be cleared.
, the file must be open for writing; with truncate
the file must be writable.
On success, zero is returned. On error, -1 is returned, and errno
- Search permission is denied for a component of the path
prefix, or the named file is not writable by the user. (See also
- Path points outside the process's allocated address
- The argument length is larger than the maximum file
- A signal was caught during execution.
- The argument length is negative or larger than the
maximum file size.
- An I/O error occurred updating the inode.
- The named file is a directory.
- Too many symbolic links were encountered in translating the
- A component of a pathname exceeded 255 characters, or an
entire path name exceeded 1023 characters.
- The named file does not exist.
- A component of the path prefix is not a directory.
- The named file resides on a read-only file system.
- The file is a pure procedure (shared text) file that is
the same errors apply, but instead of things that can be
wrong with path
, we now have things that can be wrong with fd
- The fd is not a valid descriptor.
- EBADF or EINVAL
- The fd is not open for writing.
- The fd does not reference a regular file.
4.4BSD, SVr4 (these function calls first appeared in BSD 4.2). POSIX 1003.1-1996
. POSIX 1003.1-2001 also has truncate
, as an XSI
SVr4 documents additional truncate
error conditions EMFILE, EMULTIHP,
ENFILE, ENOLINK. SVr4 documents for ftruncate
an additional EAGAIN
The above description is for XSI-compliant systems. For non-XSI-compliant
systems, the POSIX standard allows two behaviours for ftruncate
exceeds the file length (note that truncate
specified at all in such an environment): either returning an error, or
extending the file. (Most Unices follow the XSI requirement.)