I doubt that the cgo_callback method has the type the C library
desires. from https://golang.org/ref/spec#Method_declarations:
The type of a method is the type of a function with the
receiver as first argument.
I.e., the type of cgo_callback is func(a *A, ...).
The solution is to have a proper C function callback with the correct
type signature expected by the C side and resolve the correct (a *A)
to call inside the callback. Something like:
//export _callbackfunc
func _callbackfunc(fd C.int, context unsafe.Pointer) C._error_t {
a := findA(context) // resolves the correct *A based on the context
return C._error_t(a.Callback(int(fd)))
}
On Fri, Jun 17, 2016 at 3:23 AM, <and...@breakoutcommerce.com> wrote:
> Hello,
>
> Could you guys please help me.
>
> I can't find how to export method function which belongs to some go-struct
> to C-code (cgo part) as callback. I know how to export simple function which
> not belongs to any type and use it as callback for C-function, but is it
> possibly to export method of concrete struct instance? since I need
> additional info when callback will be called from C-code. As example what
> I'm trying to explain:
>
> // extern int goCallbackHandler(int, int);
> //
> // static int doAdd(int a, int b) {
> // return goCallbackHandler(a, b);
> // }
>
> import "C"
>
> type A struct {
> ... some data which used to process callback from C-side
> }
>
> // export cgo_callback
> func (a *A) cgo_callback(...){ <-----main problem here
> }
>
> main {
> C.doAdd(...)
> }
>
> I can't modify c-side - I have only compiled library, so I don't know how to
> identify which instance of struct should be used to properly process C-call
> of go-side callback.
>
> Thanks,
> Andrey
>
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