Is it possible to pass char* between COM objects

Question

I need to modify application that is written on Delphi and C++ and uses COM. And I've seen quite often that COM wrappers always use WideString and BSTR, even though in the end dll that is used works with plain char*. So it's impossible to communicate between COM objects without unicode strings? Some links for further reading on the topic is very appreciated.

Answer 1

To pass around an 8-bit char string in COM, you can either:

• use SysAllocStringByteLen() to create a binary BSTR that holds the raw char characters as-is. The receiver can then copy the char characters as-is from the BSTR.

• use SafeArrayCreate()/SafeArrayCreateVector() to create a SAFEARRAY holding VT_UI8 elements, and then you can copy the char characters as-is into the array. You can put the SAFEARRAY inside of a VARIANT, if needed.

• wrap the char characters inside of an IStream, such as from CreateStreamOnHGlobal() or SHCreateMemStream().