Spence Green

التكرار يعلم الحمار

I work at Lilt. In addition to computers and languages, my interests include travel, running, and scuba diving. more...

Managed Assemblies, IJW, and .h Files

without comments

I solved an intersting problem yesterday, although I still cannot fully explain the solution. My project uses a mixed mode DLL to load some native binaries. I constructed the DLL as a managed assembly so that in my managed code, I can use the following:

#using "mydll.dll"

This statement–It Just Works, or IJW–imports all types. Now I had defined my exception hierarchy in a separate header common to the whole project (not just the mixed dll). The exe and dll thus had the same #include statement. I could both compile and link with this setup. When the DLL threw an exception, though, I encountered a problem. Consider this snippet:

__gc public MyException : public Exception
MyException(String *s) : Exception(s) {}

//mydll.dll, built with /LD /clr
#include "Exception.h"
myFunc() {
throw new MyException(S"BLAH");

//main.cpp, built with /clr
#include "Exception.h"
catch(MyException *e)
//This handler does not catch MyException!
catch(Exception *e)
Type *t = e->GetType();

The second exception handler illuminated the most elusive aspect of this issue. Although the first handler could not catch the exception, the second catch block showed a MyException type. I have not found a sufficient explanation for this behavior, but it must stem from the interaction of native code and MSIL in the mixed DLL.

Written by Spence

July 6th, 2005 at 7:54 am

Posted in .NET

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