Exceptions across processes

DLLs run in the same process as the application that's using them. When you load a DLL, its code is mapped into the address space of the running process and its data is copied into a new memory area in that process.

In windows, you only get a new process if you create one using CreateProcess() or implicitely when you run an executable. Doing anything across process boundaries is pretty darn difficult. Processes are isolated from each other, so eg. memory address 0x123 in process A has nothing to do with memory address 0x123 in process B. To send data from one to another, you'd have to create Pipes, Shared Files, use Window Messages or TCP/IP.


So, as long as you don't plan on using the compiled DLL with a different compiler than the one it's compiled with, you won't have any problems since there are no other processes involved ;)

-Markus-

It can work, but it's dangerous. Especially for C++ exceptions (i.e. thrown with "throw"). If you have different C++ compilers it's very likely that the way they implement exceptions is different and you either will fail to catch the exception or corrupt memory trying to handle it. Even with the same compiler and compiler version you could run into issues similiar to the problems sorrounding memory allocation between DLL's.

It's usually best to fall back to error codes when crossing DLL boundaries.

Cygon: Ahh, that makes sense. I don't really know why I thought that DLLs are spawned as a new process, I just assumed that they did.. :)

Anon Mike: Ofcourse, you right. Non-standard implementation of exceptions is a problem. I'll stick to error codes :)

Thanks!

You have things straight, which is good, but just for the record:
Exception handling in the usual sense (SEH) doesn't work per process, but per thread. If the DLL creates a new thread and it throws an exception, then it won't necessarily find its way back to the calling procedure.
We could amend this to a degree by using vectored exception handling instead of structured, but it's still a bad idea. Best stick with the error codes [wink].

Admiral