Re: [Chicken-users] pass by value and callbacks

[r]

Hello pluijzer

As i know chicken didnt have pass-by-value FFI type.
This is little bit verbose workaround. Note that you should use 
foreign-safe-lambda for callbacks from C.


(import scheme chicken foreign)

#>
typedef struct { int x, y; } Point;

typedef void (*SomeCallbackFuncType)(Point point);

void someFunc(SomeCallbackFuncType callback)
{
    Point p = {1, 1};
    callback(p);
}

static void callbackFunctionJumper(Point point)
{
   callbackFunction(&point);
}
<#

(define-external (callbackFunction (c-pointer point))
  void
  (print "Hello from callback!"))

((foreign-safe-lambda* void () "someFunc(callbackFunctionJumper);"))


> Hello chickeners,
>
> I am trying to wrap a function that accepts a function pointer with an
> argument to a struct passed by value.
> I don't know how to do this (and fear it is not possible) but maybe
> somebody else has a solution.
>
> A little example of what I mean:
>
> ----
>
> #>
> typedef struct { int x, y; } Point;
>
> typedef void (*SomeCallbackFuncType)(Point point);
>
> void someFunc(SomeCallbackFuncType callback)
> {
>      Point p = {1, 1};
>      callback(p);
> }
> <#
>
> (define-external (callbackFunction (??? point))
>    void
>    (print "Hello from callback!"))
>
> ((foreign-lambda void "someFunc" c-pointer) #$callbackFunction)
>
> ----
>
> I don't actually need the the value of the object in my callback.
> Maybe that helps.
>
> Thank you in advance,
> Pluijzer
>
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