The VO ErrorBlock

The VO ErrorBlock() function gives the possibility to set a global error handler. Unfortunately, in .NET this is not more possible as the CLR (the Common Language Runtime) does not supports such a feature.

In a .NET application you need to make extensive use of try - catch blocks and use the relative exceptions to react to runtime errors. You can set a few default handlers for otherwise unhandled exceptions, but that is far away from the VO functionality.

For compatibility, the ErrorBlock() function is there, but is not called by the .NET runtime, but it is called in the VO SDK classes. They call the ErrorBlock() function from the RECOVER blocks in the error handlers on several places. And the ErrorBlock is called inside the DB…() functions when an error occurs.

On all other places in the runtime either a normal .net exception is thrown, or the exception is catched and a FALSE returned. For example:

• Incorrect usual additions throw an exception
• Most argument errors generate an exception
• VODb operations catch an exception (the RDD system reports errors through exceptions) and return FALSE on failure (and store the exception that occurred inside the RDD in the LastRddError of the runtime state). This mimics the behavior from VO where the last RDD error was stored in a structure that you could retrieve with a call to _VoDbErrInfoPtr(). This function now returns RuntimeState.LastRDDError. If the VoDb() operation is called from a Db..() function then either false is returned or the error handler is called, depending on what the VO function did.
• Low level file operations catch an exception and return either false or F_ERROR, set FError() and store the last exception that occured which can be retrieved with FException(). This is done through the method XSharp.IO.File.setErrorState().

For more details please see the post by Robert v.d.Hulst: https://www.xsharp.info/forum/public-product/1418-dtawin-server-exceptions#10445