datamatrix.net c# example INTEROPERABILITY in C#.NET

Generation DataMatrix in C#.NET INTEROPERABILITY

The output of Listing 13-23 is as follows: System.ComponentModel.Win32Exception: The filename, directory name, or volume label syntax is incorrect at TestGetLastWin32Error() at main()

C++ exception handling can exist alongside CLR exception handling. You can use subsequent catch blocks, with C++ exceptions in some catch filters and CLR exceptions in other catch filters. Remember that in 10 you saw what happens when throwing a type that does not derive from System::Exception to code in another .NET language. In that case, the nonexception type was wrapped as a RuntimeWrappedException. Wrapping also occurs when a native type is thrown from native code it is wrapped as SEHException in C++/CLI managed code and, if not caught by a matching catch block, will be caught by catch filters that match SEHException, ExternalException (the base class of SEHException), or Exception. Listing 13-26 shows the behavior with both a throw by value and via a native pointer. Listing 13-26. Coexistent C++ and CLR Exception Handling // native_exception.cpp #include <wchar.h> using namespace System; using namespace System::Runtime::InteropServices; #pragma unmanaged class NativeException { wchar_t m_str[1024]; public: NativeException(wchar_t* s) { wcscpy_s(m_str, s); } const wchar_t* GetMessage() { return m_str; } };

void throw_native_exception(bool byval) { if (byval) throw NativeException(L"Native Exception By Value"); else throw new NativeException(L"Native Exception on Native Heap"); } #pragma managed int main() { bool byval = true; try { throw_native_exception(byval); } catch(NativeException& native_exception) { wprintf(L"Caught NativeException: %s\n", native_exception.GetMessage()); } catch(SEHException^ e) { Console::WriteLine("{0}\nErrorCode: 0x{1:x}", e->ToString(), e->ErrorCode); } byval = false; try { throw_native_exception(byval); } catch(NativeException* native_exception) { wprintf(L"Caught NativeException: %s\n", native_exception->GetMessage()); } catch(SEHException^ e) { Console::WriteLine("{0}\nErrorCode: 0x{1:x}", e->ToString(), e->ErrorCode); } }

The output of Listing 13-26 is shown here: Caught NativeException: Native Exception By Value Caught NativeException: Native Exception on Native Heap

A COM HRESULT is wrapped as an exception. It may appear as a specific exception type, such as OutOfMemoryException for the HRESULT E_OUTOFMEMORY, or, if there is no specific mapping provided, as a COMException, which has an ErrorCode property that has the original HRESULT value.

Summary

This chapter covered various aspects of interoperability interop with other .NET languages, interop with native code including P/Invoke, the various compilation modes available, and how to expose native code to other .NET languages. The text touched briefly on COM interop. You learned about the marshaling library, which simplifies conversions between native and managed types. You also saw pointer types useful in interop, such as interior_ptr and pin_ptr, native and managed entry points, the __clrcall calling convention, double thunking and how to avoid it, how to include a native class in a managed class, how to include a managed class in a native class with gcroot and auto_gcroot, and finally, how exceptions and errors in native code surface in managed code. This completes our study of the foundations of the C++/CLI language extensions. Of course, there is much more to learn about the .NET Framework and programming for the CLR, and there are numerous libraries to explore. Now that you have learned enough to get started with C++/CLI code and interoperability technologies, you ll want to apply this knowledge to your own domain, whether that s creating a hybrid MFC and WPF application, writing a game, or simply using a legacy native library in your managed application. You ll want to keep this book handy as a reference to the core language as you apply this technology to your own unique programs. I ve included a few additional notes in the appendix and a syntax summary that should be helpful when writing C++/CLI code.

his appendix covers the new keywords introduced in C++/CLI, specifies which are also reserved words, and defines and lists contextual keywords and whitespace keywords. This appendix includes a reference table for features available in native, mixed, pure, and safe modes. You ll also find a summary of the syntax introduced in C++/CLI.