On Tue, Apr 11, 2017 at 2:25 AM, hui zhang <fastfad...@gmail.com> wrote:
>
> If I define the same 2 struct in c and go
> can they be passed directly with unsafe.Pointer
The struct layout rules are under-defined in Go. The current rules
are straightforward, and it is the case that most structs with the
same sequence of field types will look the same in C and Go. Of
course you must remember that `int` in Go is often not the same size
as `int` in C. Also the alignment rules are not always the same, so
don't permit any alignment padding. And this may change in future Go
releases.
> and how to export go struct from go to c ?
You can't, not easily. But it's easy to use cgo to export a C struct
from C to Go, and doing that avoids all the concerns about types and
alignments, so you should do that if at all possible.
> /*
> #include <stdio.h>
>
> typedef struct {
> int a;
> int b;
> } Foo;
>
> void pass_struct(Foo *in) { printf("%d : %d\n", in->a, in->b); }
>
> */
>
> import "C"
>
> import (
> "fmt"
> "unsafe"
> )
>
> type Foo struct{ a, b int32 }
>
> C.pass_struct((*C.Foo)(unsafe.Pointer(&foo)))
For example, how about `type Foo C.Foo`?
Ian
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