truncate or extend a file to a
char *path, off_t
causes the file named by path or referenced by
fd to be truncated or extended to
length bytes in size. If the file was larger than this
size, the extra data is lost. If the file was smaller than this size, it
will be extended as if by writing bytes with the value zero. With
the file must be open for writing.
Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the error.
ftruncate() will succeed unless:
- The length is a negative value.
- The length exceeds the maximum file size of the underlying filesystem.
- An I/O error occurred updating the inode.
truncate() may return the
- A component of the path prefix is not a directory.
- A component of a pathname exceeded
NAME_MAXcharacters, or an entire pathname (including the terminating NUL) exceeded
- The named file does not exist.
- Search permission is denied for a component of the path prefix.
- The named file is not writable by the user.
- Too many symbolic links were encountered in translating the pathname.
- The named file is a directory.
- The named file resides on a read-only file system.
- The file is a pure procedure (shared text) file that is being executed.
- path points outside the process's allocated address space.
ftruncate() may return the following
- The fd is not a valid descriptor.
- The fd references a socket, not a file.
- The fd is not open for writing.
ftruncate() functions conform to
IEEE Std 1003.1-2008 (“POSIX.1”).
ftruncate() system calls first appeared in
These calls should be generalized to allow ranges of bytes in a file to be discarded.
truncate() to extend a file is not