dear uffi-dev,
Is there a way to use UFFI to get access to data in a struct such as
the following:
typedef struct array_struct {
unsigned char stuff[80];
unsigned int other_stuff[80];
} array_struct;
I can't figure out how to do the UFFI declaration of the struct to be
able to access stuff and other_stuff.
Thanks,
Cyrus
dear uffi-devel, I know there's been some discussion of how to avoid runtime allocation on SBCL for UFFI memory access, but I'm trying to declare an UFFI function that returns a :pointer-void and I get a warning about runtime allocation. Declaring the return type as :int makes the warning go away, but this is, of course, not the right answer. Is there a way to do this without the runtime allocation? Thanks, Cyrus
Dear uffi-devel, I have a few more questions about c-strings and foreign strings. What exactly is a c-string? I assumed this was a string that one would pass to a C function that takes a string, but apparently, at least for SBCL, this is instead a foreign-string. Furthermore c-strings are basically no-ops. Is this intended? Also, the with-foreign-string macro seems very useful but is undefined (at least it's not in the pdf file). Furthermore, there is a handy-dandy with-cstrings, but not a with-foreign-strings which would seem to also be useful. Thanks, Cyrus
Hi Cyrus, uffi-devel. On Thu, Mar 10, 2005 at 01:21:13PM -0800, Cyrus Harmon wrote: > I know there's been some discussion of how to avoid runtime allocation > on SBCL for UFFI memory access, but I'm trying to declare an UFFI > function that returns a :pointer-void and I get a warning about runtime > allocation. Declaring the return type as :int makes the warning go > away, but this is, of course, not the right answer. Is there a way to > do this without the runtime allocation? Not easily with UFFI currently. If you look at my correspondence with kmr on this list a few months ago, I think I cover all the bases of what's happening. I'm using a workaround in a game that I intended to release a while ago, but which I haven't finished, and I'm currently on a vacation from programming. If you're interested in working on a solution (other than my workaround), I'd like to hear about it. I was toying with a few ways of getting UFFI to deal with the problem cases nicely, but it might require some overhaul to do the Right thing. Sorry I can't be of more help just right now. Hopefully I'll be getting back to hacking on lisp stuff in a week or two. -- -- Julian Squires
Cyrus Harmon wrote: > I know there's been some discussion of how to avoid runtime allocation > on SBCL for UFFI memory access, but I'm trying to declare an UFFI > function that returns a :pointer-void and I get a warning about runtime > allocation. Declaring the return type as :int makes the warning go > away, but this is, of course, not the right answer. Is there a way to > do this without the runtime allocation? Not every runtime allocation warning causes SBCL/CMUCL to have horrible performance. I've not tested with a function returning :pointer-void, but typically that wouldn't cause a problem. The runtime problem with SBCL/CMUCL is when you'd want to cast that pointer to another type. What are you planning on doing with the return value? Just passing back to a foreign function, or casting and dereferencing? If it's the first, have you tested if there really is a performance problem [it'll be easy to see if it is]. In the latter case, SBCL/CMUCL have serious trouble with this and you and I have exchanged email before how to try to work around that. -- -- Kevin Rosenberg kevin@...
Cyrus Harmon wrote: > I have a few more questions about c-strings and foreign strings. What > exactly is a c-string? I assumed this was a string that one would pass > to a C function that takes a string, but apparently, at least for SBCL, > this is instead a foreign-string. Furthermore c-strings are basically > no-ops. Is this intended? What exactly c-string is depends upon the implementation, so you should consider it an opaque type. It's an optimization type which on some platforms is a no-op and on other platforms is a foreign-sring. On SBCL/CMUCL, cstrings themselves are normal lisp strings: UFFI(3): (convert-to-cstring "foo") "foo" On Allegro, a cstring is a foreign string UFFI(7): (convert-to-cstring "foo") 2684436496 > Also, the with-foreign-string macro seems very useful but is undefined > (at least it's not in the pdf file). Furthermore, there is a > handy-dandy with-cstrings, but not a with-foreign-strings which would > seem to also be useful. with-foreign-string is exported from the UFFI package and is included in the test suite. It should be added to the documentation. Yes, adding a with-foreign-strings macro would be useful and would be add symmetry to with-cstrings.(Continue reading)
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