Does this conform to your understanding of the specs?

Yes.(More precisely, with my assumption about which of the OP's examples is wrong.) I think that's almost equivalent^† to my much more verbose, probably slower, certainly uglier c-style function. Very nice. ++

† It would be completely equivalent except that yours won't work on arbitrary binary data since you require a unique character not otherwise present in the strings to build your concatenation. That obviously wouldn't pose a problem for the OP, however.

-sauoq
"My two cents aren't worth a dime.";