C++ optional parameters in WinRT

Question

Hello,
We have WinRT component referring C++ code.
C++ code has optional parameters.
WinRT code is projected for C#.

Code details:
Current code without proper handling of optional parameters.

example.idl

namespace Test
{
[default_interface]
runtimeclass example
{
void login(String authCode, String emailId);
}
}

example.cpp

namespace winrt::Test::implementation
{
void example::login(hstring const& authCode, hstring const& emailId)
{
//I need to call below C++ API here
//DLLExport void login(std::optional<std::string> authCode, std::string emailId);
}
}

example.h

namespace winrt::Test::implementation
{
struct example: exampleT<example>
{
void login(hstring const& authCode, hstring const& emailId)
}
}

C# projection(cswinrt.exe) is done for this IDL file(winmd)
How can I know "authCode" is optional in C#? so that accordingly I can pass.
How to handle optional parameters across ABI.

Answer 1

Hello,
Welcome to Microsoft Q&A!

C++ string optional parameters in WinRT

I have to say In the Windows Runtime, strings are value types. “null” is treated as an empty string. If an empty string (“”) is not a valid authCode, then you can use an empty string to represent “no authCode”. Otherwise, you will have to express the optionality in some other way, such as a separate Boolean parameter or an overload.

Thank you.

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