This begs the question how syscalls are handled. I assume they don't use
cgo, but often they require to pass a pointer to some memory which is
documented as a C-struct. Is there any guidance on that (or any problems
that might arise there)?
On Tue, Apr 11, 2017 at 6:41 PM, Ian Lance Taylor <i...@golang.org> wrote:
> 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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