Raising Exceptions in C++11
To throw an exception from an operation implementation, you simply instantiate the exception, initialize it, and throw it. For example:
void Filesystem::FileI::write(Filesystem::Lines text, const Ice::Current&) { // Try to write the file contents here... // Assume we are out of space... if(error) { throw Filesystem::GenericError("file too large"); } }
No memory management issues arise in the presence of exceptions.
If you throw an arbitrary C++ exception (such as an int
or other unexpected type), the Ice run time catches the exception and then returns an UnknownException
to the client.
The server-side Ice run time does not validate user exceptions thrown by an operation implementation to ensure they are compatible with the operation's Slice definition. Rather, Ice returns the user exception to the client, where the client-side run time will validate the exception as usual and raise UnknownUserException
for an unexpected exception type.
If you throw a run-time exception, such as MemoryLimitException
, the client receives an UnknownLocalException
. For that reason, you should never throw Ice run-time exceptions from operation implementations. If you do, all the client will see is an UnknownLocalException
, which does not tell the client anything useful.
Three run-time exceptions are treated specially and not changed to UnknownLocalException
when returned to the client: ObjectNotExistException
, OperationNotExistException
, and FacetNotExistException
.