checksum

[CharlieP]

Every once in a while I get a message "Warning[src\object.c:288 (Object_load_packed)]:  Checksum mismatch from packed object: autocars"

The end object sometimes changes depending on what game I am working on (MetRHtAr)

1.  What is this and is anything to worry about.

2.  How can I remedy this issue?

[Broxzier]

That means that there is an object with an incorrect checksum. This means that the file you have, probably called autocars.DAT in your ObjData folder, is invalid, but since you have the option to allow loading objects with an incorrect checksum enabled you can load them anyway.

[imlegos]

So, this doesn't really mean anything.

[X7123M3-256]

This error message means the save file contains a packed object whose checksum does not match the contents of the file. In theory, this indicates that the object has been corrupted, and the game stops loading of that object.

In practice, there is usually nothing wrong with the object, it just has the wrong checksum. This is because some custom objects include nonzero bytes in locations that are zeroed by the loader - these bytes are zeroed when the object is loaded, but the checksum is not updated. When the object is packed into the save file, it has the wrong checksum. When you reopen the park, you see this message.

If you already have the object installed then the object is loaded from your ObjData folder anyway, and this is just a warning. If you do not have the object installed the object load will fail and you will be unable to open the park (unless you have "Allow loading with incorrect checksums" enabled, which disables this check entirely). OpenRCT2, unlike vanilla, does recalculate the checksum of objects upon saving - this was supposed to fix the issue but it doesn't work in all cases.

As long as you are able to load the park then this message can be ignored for the most part, but if you are sharing the park online you should also upload copies of all the objects that aren't exporting so that those who don't have them can install them. This is especially important if you expect the park to be opened in vanilla, which doesn't allow bypassing the checksum test.

Edited May 3, 2016 by X7123M3-256

[CharlieP]

All of these rides were ones that were found in other's parks or downloaded on line. Can the checksums be corrected?

[X7123M3-256]

The checksums can be corrected by some care is required. If you recalculate the checksum to match the modified file, the ride will become exporting but it will not be treated as the same ride - you end up with two copies, and existing parks will continue to load the broken one.

The solution I use is to instead tack on some extra bytes in order to make the original checksum correct again. Then the original file can be replaced by the corrected version and the game will not notice. OpenRCT2 is supposed to do this correction automatically, but it does not always work properly.

As a rule of thumb, tracked rides that aren't my own are usually created in Buggy's ridemaker, and hence unexporting. Flat rides do not trigger the bug and so should always work. If you do not get this error message when loading the park, then either all rides exported properly, or the park was not exported at all.