Function

ftrunc invokes the ftrunc callable service to change the size of the file identified by the file descriptor.

Parameters

fd

The file descriptor (a number) for the file.

file_size

The new size of the file, in bytes.

Usage notes

1. The ftrunc service changes the file size to file_size bytes, beginning at the first byte of the file. If the file was previously larger than file_size, all data from file_size to the original end of the file is removed. If the file was previously shorter than file_size, bytes between the old and new lengths are read as zeros.
2. Full blocks are returned to the file system so that they can be used again, and the file size is changed to the lesser of file_size or the current length of the file.
3. The file offset is not changed.