[plt-scheme] strings?

I'm trying to add an extension to mzscheme. In
the scheme code I do something like (sqlite:open "dbname").
In the extension code I check for SCHEME_CHAR_STRINGP(argv[0]),
and then I extract with char *p = SCHEME_BYTE_STR_VAL(argv[0]);
I only get the first character of the actual string, the
string is needed to pass to sqlite_open().

How do I structure this code? It seems really odd
that I test with CHAR_STRINGP but extract with
BYTE_STR_VAL.

Mike