Truncate a file: Difference between revisions

The task is to demonstrate how to truncate a file to a specific length. This should be implemented as a routine that takes two parameters: the filename and the required file length (in bytes). The truncation can be achieved using system or library calls intended for such a task, if such methods exist, or by creating a temporary file of a reduced size and renaming it, after first deleting the original file, if no other method is possible. The file may contain non human readable binary data in an unspecified format, so the routine should be "binary safe", leaving the contents of the untruncated part of the file unchanged. If the specified filename does not exist, or the provided length is not less than the current file length, then the routine should raise an appropriate error condition and exit. On some systems, the provided file truncation facilities also extend the file, if the specified length is greater than the current length of the file. For the purpose of this task, it is permissible for such facilities to be used. A note should made against the provided solution if an increase in length occurs and optionally a warning message relating to the increase in file size may be implemented.