[cffi-devel] Passing struct by value, kind of
Hello lispers! I know that CFFI doesn't support passing structs by value. What I'm wondering is, is it possible to squeeze in a small struct by instead passing it as an int (or something) of the same size as the struct? Example: struct MyStruct { int32 x, y; }; int myFunction(struct MyStruct s); Could I force/lie to CFFI and declare 's' to be of type int64 and pass it that way? I tried something similar, but then CFFI (well, ClozureCL) just couldn't resolve the function symbol.. -- Markus Flambard 6A63 2761 0A9E E510 DDAF C796 A3DF AB90 9C7C AD5C
With some test I found that it is indeed possible. The unresolved symbol problem was unrelated. Thanks for listening! :-) -- Markus Flambard 6A63 2761 0A9E E510 DDAF C796 A3DF AB90 9C7C AD5C
On Sun, Jul 27, 2008 at 12:20 PM, Markus Flambard <markus@flambard.se> wrote:
I know that CFFI doesn't support passing structs by value. What I'm wondering is, is it possible to squeeze in a small struct by instead passing it as an int (or something) of the same size as the struct?
On linux/x86, for instance, it's fairly straightforward to pass structs by value since all arguments are passed on the stack, word-aligned. For instance, given the following C code: /* sizeof(s) => 12 */ struct s { char c; short s; int i; }; void f(char x, struct s y, short z); f can be declared as: (defcfun f :void (x :char) (y0 :int) (y1 :int) (z :short)) f(1, {2, 3, 4}, 5) is then equivalent to (f 1 #x00030002 4 5), or something like that. This works for any struct regardless of its size or its members' data types. Other architectures might have less straightforward calling conventions. -- Luís Oliveira http://student.dei.uc.pt/~lmoliv/
participants (2)
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Luís Oliveira -
Markus Flambard