Languages-CPP.md

C++

DO implement types using C++ and C++/WinRT

DO follow the CppCoreGudelines for all new code.

DO enable /W4 /Wx for all new code.

CONSIDER using the Windows Implementation Library for Windows-specific helpers rather than creating your own.

DO use 4-space indentation instead of tab characters.

Catching C++/WinRT Exceptions and HRESULT

Exceptions should not be used for standard flow control.

When a catch clause is required, note that winrt::hresult_error does not also catch std::bad_alloc or any of the other C++ standard exceptions. In cases where a single catch handler desires to pull out an HRESULT, use the following:

// For code using C++/WinRT
catch (...)
{
    auto e{ winrt::hresult_error(winrt::to_hresult(), winrt::take_ownership_from_abi) };
    auto hr{ e.code() };
    auto message { e.message() };
    // hr contains the WinRT exception or best-guess conversion from a C++ exception,
    // message contains the best-guess textual format of that exception
}

// For code using WIL
catch (...)
{
    auto hr{ wil::ResultFromCaughtException() };
    // hr contains the WinRT exception, WIL exception, or best-guess conversion from a C++ exception
}

C++/WinRT's ABI layer automatically catches and converts exceptions generated during a method call and uses a similar mechanism to map a C++ exception to an HRESULT that can be delivered across the ABI.