Visual C++ WinRT FAQ – WRL vs C++/CX

As I said in my previous blog entry, WRL is a non-extension-based ISO compliant alternative to using C++/CX when targeting WinRT. They are both far easier to use than using straight COM, so what do you choose to use for your Visual C++ WinRT needs. In his talks, Herb Sutter has very strongly recommended that we use C++/CX. And it’s fairly obvious that C++/CX is far simpler to use than WRL, specially when creating components (consuming components is relatively easier).

  • The big thing with WRL is that you can use ISO C++. You don’t have to learn a new syntactic extension that you cannot use outside the Microsoft-world. Most C++ devs would feel comfortable using WRL, specially if they’ve used ATL before. That said portability is a myth, since WRL code is as tied into Windows as would be C++/CX code.
  • Do you want to totally avoid exceptions (perhaps to remain in sync with existing code that doesn’t use exceptions)? If so, you have to use WRL since C++/CX uses exceptions.
  • Performance wise, will you see any difference? As stated above, C++/CX uses exceptions while WRL uses HRESULTs. So the performance implications of using exceptions will obviously come into play. There is also the non-trivial conversion between HRESULTs and RT exceptions. Outide of that, I don’t think there’s going to be any noticable difference in performance
  • Not sure to what extent you can do this, but since WRL exposes the underlying COM architecture, you can fine-tune your code to some degree (since WinRT is built on top of COM). I haven’t read or heard about any scenarios where this has actually made a difference.
  • The psycological aspect. While this is the least technical of the reasons, it might be the biggest factor here. Many C++ devs would simply hate anything that they see as foreign syntax. And C++/CX is certainly not ISO C++. Its close similarity with C++/CLI (which many C++ devs found disgusting) doesn’t help either. If your C++ dev team comprises mainly of a bunch of these guys, I reckon it’d be wise to just use WRL.

And personally speaking, I’d probably recommend that you learn to use both C++/CX and WRL. That way you can use what’s best for your specific scenario. And finally, you can mix WRL and C++/CX in the same project.

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