Linux C ftruncate 函式清空檔案注意事項（要使用 lseek 重置偏移量）
阿新 • • 發佈：2019-01-08
DESCRIPTION
The truncate() and ftruncate() functions cause the regular file named by path or referenced by fd to be truncated to a size of precisely length bytes.
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 null bytes ('\0').
The file offset is not changed.
If the size changed, then the st_ctime and st_mtime fields (respectively, time of last status change and time of last modification; see stat(2)) for the file are updated, and the set-user-ID and
set-group-ID permission bits may be cleared.
With ftruncate(), the file must be open for writing; with truncate(), the file must be writable.
The truncate() and ftruncate() functions cause the regular file named by path or referenced by fd to be truncated to a size of precisely length bytes.
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 null bytes ('\0').
The file offset is not changed.
If the size changed, then the st_ctime and st_mtime fields (respectively, time of last status change and time of last modification; see stat(2)) for the file are updated, and the set-user-ID and
set-group-ID permission bits may be cleared.
With ftruncate(), the file must be open for writing; with truncate(), the file must be writable.