Question

I have C++ project with functions:

_API void __stdcall  InstallMailHandler(MailHdlPtrType Hdl)
{ ... }
_API void __stdcall  UninstallMailHandler(MailHdlPtrType Hdl)
{ ... }

typedef void (STDCALL  *MailHdlPtrType)(unsigned char instNo, bla bla bla);

And I have in C#:

public static extern void InstallMailHandler(MailHdlPtrType Hdl);
public static extern void UninstallMailHandler(MailHdlPtrType Hdl);

public delegate void MailHdlPtrType(byte instno, bla bla bla);

But when I call InstallMailHandler and UninstallMailHandler from C# with the same function in arguments, it results in different addresses in C++ so it cannot uninstall previously installed mail handler.

Is it possible to somehow ensure that both invokes will result in the same function address, or maybe set an address explicitly?

Answer 1

I think the problem is that the new delegate object is created in each call.

You probably call them like that:

InstallMailHandler(new MailHdlPtrType(YourCoolFunction));
// ...
UninstallMailHandler(new MailHdlPtrType(YourCoolFunction));

or in equivalent short form:

InstallMailHandler(YourCoolFunction);
// ...
UnnstallMailHandler(YourCoolFunction);

I think you just need to keep the same delegate:

MailHdlPtrType my_deleg = new MailHdlPtrType(YourCoolFunction); // this may be field in your class or something
//...
InstallMailHandler(my_deleg);
// ...
UnnstallMailHandler(my_deleg);