Or one 'old world' technique some win APIs use Pass in a null and the call tells you what size buffer you need, create it and pass it in on a second call.
Mike On Tue, Nov 26, 2019, 11:53 Tony McGee <tmcgee...@gmail.com> wrote: > You could return a BSTR and let the interop marshaling do clean up for > you: > > > https://www.codeproject.com/Articles/1189085/Passing-strings-between-managed-and-unmanaged-code > > > > On Tue, 26 Nov. 2019, 11:09 Greg Keogh, <gfke...@gmail.com> wrote: > >> >> msg is a stack variable, you can't return it iirc. Either create a var on >>> the heap, or pass msg in as a parameter. >>> >> >> D'oh! You're right. I changed the code to the following and it's working. >> Notice use of CoTaskMemAlloc, which I think is the least worst choice of >> heap allocation functions according to the MSDN docs. >> >> Notice that I've completely forgotten what the lengths are supposed to be >> for string lengths, is it x2 for wchar? is it correct to allocate 200 bytes >> for 100 wchars? The compiler is giving me an overrun warning. You're >> supposed to use sizeof or something like that, but my brain has gone mushy >> on all those rules now (which is part of the reason I never want to code >> this assembler crap again!). >> >> Even worse … what about the memory leak in CoTaskMemAlloc? I make the >> buffer, copy in the string and return it, but it's now leaked. Should I use >> a global static buffer that can be released later? When? >> >> *GK* >> >> [image: image.png] >> >> >>
