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C++ is Coming to .NET Core for Windows

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Microsoft has announced plans to offer C++/CLI in .NET Core 3.1. This would only be offered for Windows applications; you won’t be able to use C++/CLI for Linux or OSX.

C++/CLI is Microsoft’s second attempt at creating a version of C++ that can target .NET. Created in 2005, it replaced Managed Extensions for C++. The purpose is to allow developers to freely mix managed (i.e. .NET) objects with traditional C++ objects.

The first use case that comes to mind is interoperability. While VB and C# can directly call native DLLs and COM components, those libraries don’t always offer an appropriate API. By wrapping them in a C++/CLI library, abstractions can be put into place that hide the incompatibilities.

Another use is direct hardware access. When working with hardware, developers often need to carefully manipulate unmanaged memory. C# allows this in “unsafe” blocks, but only to a limited degree. C++, on the other hand, can use inline assembly to get around any language-based limitations.

There are restrictions here. Hans Passant explains,

The C++/CLI compiler supports generating both machine code and IL. It will generate machine code for any code that is compiled without /clr in effect or functions that are bracketed with #pragma managed(push, off) and #pragma managed(pop). Or functions that must be compiled to machine code because they contain code that cannot be translated to IL. Like _asm, note the C4793 warning you got for the first snippet. Suppress the warning with #pragma managed. Such code cannot use any managed types of course.

The unit of code generation is a function. What cannot work is a function that needs both. Your main() function must be compiled to IL because it uses managed types. The function won't be inlined of course.

Presumably because the Microsoft Visual C++ compiler only targets Windows, C++/CLI likewise can only target Windows. This mixing of native and IL code would require a platform-specific compiler for each operating system.

This is not an impossible goal. C++/CLI has been standardized as ECMA-372. So in theory LLVM or gcc could adopt the extension and offer a Linux or OSX version.

Other C++/.NET Languages

While C++/CLI is still a viable option, it wasn’t Microsoft’s last attempt. As part of Windows 8 and the WinRT initiative, Microsoft created C++/CX. This resembles the C++/CLI syntax, but was designed specifically to work with WinRT’s version of COM.

In 2015, C++/CX was replaced with C++/WinRT. Unlike the other languages discussed in this article, C++/WinRT isn’t an extension to C++. Based on C++ 11 and 14, developers can now write ‘normal’ C++ code while still accessing the WinRT/COM infrastructure. For more information, see CppCon 2016: Kenny Kerr & James McNellis “Embracing Standard C++ for the Windows Runtime.

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