Question

What am I missing here? I thought that the ^ was a smart pointer and that I could pass string by ref to a function. What about other hat objects?

// calling code
MyClass::GetString(_str1, _str2);
// both strings are nullptr at this point

/* static */ 
MyClass::GetStrings(String^ str1, String^ str2)
{
    // Read from Local Settings
    auto value = localSettings->Values->Lookup(kKey);
    String^ temp = ref new String(value->ToString()->Data());
    str1 = temp;

    // same for str2
}

Answer 1

A T^ is similar to a pointer type; when you have a function with a T^ parameter (like your GetStrings static member function), the hat is passed by value, just like a pointer is passed by value.

If you want the String^‘s passed by reference, you need to use references:

void MyClass::GetStrings(String^& str1, String^& str2)

Note that references are a C++ language feature and are not part of the Windows Runtime type system. The Windows Runtime type system also does not support in/out by reference parameters; only out parameters are supported.

Therefore, if MyClass is a public Windows Runtime reference type and GetStrings is a public or protected member function (basically, if MyClass::GetStrings appears in metadata and is callable across the Windows Runtime ABI), you need to use pointers:

void MyClass::GetStrings(String^* str1, String^* str2)

These pointers are out parameters: you can write to the pointed-to String^s but you cannot read from them.