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From: | Kristian Lein-Mathisen |
Subject: | Re: [Chicken-hackers] incorrect warning during compilation |
Date: | Fri, 27 Jun 2014 16:30:22 +0200 |
> Oh, I see. I though it was meant to be used interchangeably. I can't useYou could also keep everything as it is and ignore the warning, but I
> string->blob, though, because that will copy the data and I need to modify
> it from C. What foreign type should I use for this sort of thing?
>
> - (c-pointer char) with (location "string") works, but is a lot of typing
>
> - scheme-pointer seems to work, but:
>
> requires type cast in C:
>
> (print ((foreign-lambda* c-string ((scheme-pointer x)) "((char*)x)[0] = 65;
> return(x);") "xBC"))
>
> allows all types, I just want blob/string:
>
> (print ((foreign-lambda* c-string ((scheme-pointer x)) "((char*)x)[0] = 65;
> return(x);") 45.0))
>
> is there a "string" foreign type that works like "blob", that provides a
> (char*) argument and checks that argument is a string? Or is there a
> string->blob/shared procedure anywhere?
understand that it isn't the cleanest solution. I'm not aware of any
documented interchangability between strings and blobs, it is an
implementation artefact. "string->blob/shared" would make sense but is
not possible in the current implementation (srfi-4 vectors have an
indirection to the raw data buffer, there this conversion only changes
the wrapper object, but strings and blobs contain the data without the
indirection.)
So, I can't think of a solution that answers all of your questions.
I would go with the scheme-pointer.
We could add another foreign type, that accepts strings but doesn't
copy. I'll look into that.
felix
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