I\'m loading a dll (c#) from QTP. Is it possible to debug the c# code when the qtp test starts.
Yes you can debug into the dll's you can, but you will need source (unless you want to look at the disassembly) and you will also need the PDBs (debug symbols) for the assembly. It is pretty easy to setup...
NOTE: if the breakpoint is not hit, VS probably can't find the PDB's and you either need to add a path in options in VS (or something so it can find them).
Also, try turning off "Enable just my code" in the Tools->Options->Debugging options page if it is still not working (mostly if you are looking at release built code).
Update: Answering comment... If you go to Tools->Options... Select "Debugging" on the list on the left and expand that, then select "Symbols" you can add paths there for VS to search for symbols. Also, if you don't have the exact symbols you can right-click the breakpoint and select location and check the option that will allow the symbols to be out of sync.
Hope this helps!
You can insert a call to Debugger.Break()
and run the external application, when the break point will be reached Windows will offer you to debug the exception.
Choosing debug will enable you to run the code after the break inside Visual Studio and set break points inside your code.
In case you're using Vista/Win7 you might need to enable debugging - have a look at this post to learn how.