There is an amusing comment in the CLR about it's support for odd length BSTRs[0]. There can be an extra wchar after the null terminator to store the extra byte

There is an amusing comment in the CLR about it's support for odd length BSTRs[0]. There can be an extra wchar after the null terminator to store the extra byte. It looks like if you use the automatic BSTR marshaler it creates a copy[1], though the CLR is so big it's hard for me to say that with confidence. Taking the address of a string with the fixed statement in C# of course won't allocate and that pointer can be passed to APIs that expected Unicode strings. [0]: https://github.com/dotnet/coreclr/blob/a123c3972c447c8bcfa1810fde0c7ffb842fa31b/src/vm/object.cpp#L1853-L1869 https://github.com/dotnet/coreclr/blob/a123c3972c447c8bcfa18... [1]: https://github.com/dotnet/coreclr/blob/a123c3972c447c8bcfa1810fde0c7ffb842fa31b/src/vm/olevariant.cpp#L5250-L5275 https://github.com/dotnet/coreclr/blob/a123c3972c447c8bcfa18...