Corrupted programs

[David H]

I have used various programmes and one in particular broke down over time until it was unusable. It was an accounting program that worked for a while and then started duplicating entries and whole months. It's not possible to open them to interfere with the code so how do they deteriorate over time if just made up of strings of code?

[rojash]

It's unlikely that the program itself is corrupted - only the data. Most accounting programs store their data in some form of relational database. When you enter data it is stored in a buffer, and when the buffer is full, the information is written back to the hard disk. Both the program itself and your operating system have a hand in operating the buffers. An example of how corruption can occur is as follows:
The main data file has relatively large records so its buffer fills quickly and is written back to the disk. The index file has small records so the buffer is written back less frequently. If you switch off your machine without closing down properly (e.g. there is a power cut), some buffers may be written and others not. at this point the indexes will be out of synch with the true state of the data in the files. Worse, if the power cut occurs during the actual write process, the files may be corrupted.
From this point on the program will act strangely - not because it is damaged, but because its data files are. What's more, if you continue to use the program, the corruption can spread rather like a cancer.
Most programs of this type have a utility for detecting and repairing damaged data files, but a good backup regimen is the real way to protect your data.

[David H]

Good stuff Rojash. While I'm here, a specific current problem with the new version is every so often it calculates VAT at random amounts instead of applying 17.5% automatically.

It isn't crazy enough for the difference to be noticeable but gives trhe inspector something to moan about when they pick it up. Is this just another version of the same problem I wonder? (I am reporting it to the developers as well of course!).

[rojash]

Difficult to answer that one without knowing the underlying architectur. It's possible, but it sounds more like a bug.