<bargarply@yahoo.com>

On 24-Feb-09, at 8:41 AM, John Thompson wrote:

> Hi,
> 
> I'm trying to get a toy, loadable C++ library compiled.  My setup is
as follows:
> 
> foo.scm:
> 
>  (define bar (c-lambda (char-string) int "cpp_bar"))
> 
> foo.cpp:
> 
> int cpp_bar(char* text) {
>   return 0;
> }
> 
> foo.h:
> 
> int cpp_bar(char* text);

In C++, prototypes are not optional (and if it works in C it is by accident). 
In the C++ code generated for foo.scm the C++ compiler has no idea what is the
prototype of cpp_bar that you want to call.  You might think that the c-lambda
types are there to supply that information, but in fact the Gambit compiler
simply generates a call to cpp_bar whose *actual* parameters are those of the
c-lambda.  By not automatically
 generating
 a prototype for cpp_bar it allows for
cpp_bar to be a macro or a qualified name such as "cpp::bar" or inline
code such as "___result = ___arg1[0];".  So to solve your problem
foo.scm should be

(c-declare #<<end-of-c-declare
#include "foo.h"
end-of-c-declare
)

(define bar (c-lambda (char-string) int "cpp_bar"))

Note that you'd have to include foo.h if this was a C++ module, for exactly
the same reasons, so it shouldn't be too surprising.

Marc