Hi Ian,
It is working now. Thank you so much for a quick response.
Ami
On Saturday, July 24, 2021 at 12:31:00 AM UTC+5:30 Ian Lance Taylor wrote:
> On Fri, Jul 23, 2021 at 10:39 AM Ami Ladani <ami.l...@cohesity.com> wrote:
> >
> > Hi Ian,
> > I tried to merge both go files as you suggested and it is showing same
> error as the previous one.
> > Following is the code. Also, I would like to mention that I am using
> Go1.15 linux/amd64.
> >
> > $CGO_ENABLED=1 go build .
> > # _/home/ami.ladani/Downloads/experiment
> > ./main.go:22:44: baz_ptr.b undefined (type *GoBaz has no field or method
> b)
> > ./main.go:23:44: baz_ptr.f undefined (type *GoBaz has no field or method
> f)
> >
> > // c_header.h
> > typedef void (*cb)(void* qux, int status, void *command_data, void
> *cb_data);
> > typedef struct{
> > int a;
> > int b;
> > } Foo;
> > typedef struct{
> > char* ch;
> > cb callback;
> > } Bar;
> > typedef struct{
> > Foo* f;
> > Bar* b;
> > } Baz;
> > Baz* allocateBaz(){
> > Baz* baz = malloc(sizeof(Baz));
> > Bar* bar = malloc(sizeof(Bar));
> > Foo* foo = malloc(sizeof(Foo));
> > baz->f = foo;
> > baz->b = bar;
> > return baz;
> > }
> >
> > //main.go
> > package main
> > /*
> > #include <stdio.h>
> > #include <stdlib.h>
> > #include <stdint.h>
> > #include <string.h>
> > #include "c_header.h"
> > */
> > import "C"
> > import "unsafe"
> > type GoBaz C.struct_Baz
> > type GoBar C.struct_Bar
> > type GoFoo C.struct_Foo
> >
> > func main() {
> > baz_ptr := (*GoBaz)(unsafe.Pointer(C.allocateBaz()))
> > bar_ptr := (*GoBar)(unsafe.Pointer(baz_ptr.b))
> > foo_ptr := (*GoFoo)(unsafe.Pointer(baz_ptr.f))
> > }
>
> Ah, you're right, I missed something. The C code says
>
> typedef struct{
> int a;
> int b;
> } Foo;
>
> The Go code says
>
> type GoFoo C.struct_Foo
>
> That's not right. In Go C.struct_Foo refers to the type defined in C
> as "struct Foo". But there is no such type in your C header. There
> is only the typedef of an anonymous struct to Foo. The way to refer
> to that in Go is "C.Foo". If I remove the "struct_" from your Go code
> then it works for me.
>
> Ian
>
>
> > On Friday, July 23, 2021 at 3:43:19 AM UTC+5:30 Ian Lance Taylor wrote:
> >>
> >> On Thu, Jul 22, 2021 at 2:53 PM Ami Ladani <amila...@gmail.com> wrote:
> >> >
> >> > I am trying to access members of a C struct from go. Compiler is
> showing structure's members are undefined. I have attached my code and the
> error message below.
> >> >
> >> > Please have a look and help if you can.
> >> >
> >> > $CGO_ENABLED=1 go run main.go cfuncs.go
> >> > # command-line-arguments
> >> > ./main.go:18:44: baz_ptr.b undefined (type *GoBaz has no field or
> method b)
> >> > ./main.go:19:44: baz_ptr.f undefined (type *GoBaz has no field or
> method f)
> >> >
> >> > //c_header.h
> >> > typedef void (*cb)(void* qux, int status, void *command_data, void
> *cb_data);
> >> > typedef struct{
> >> > int a;
> >> > int b;
> >> > } Foo;
> >> >
> >> > typedef struct{
> >> > char* ch;
> >> > cb callback;
> >> > } Bar;
> >> >
> >> > typedef struct{
> >> > Foo* f;
> >> > Bar* b;
> >> > } Baz;
> >> > //--------------------------------
> >> >
> >> > //cfuncs.go
> >> > package main
> >> > /*
> >> > #include<c_header.h>
> >> > #include <stdlib.h>
> >> >
> >> > Baz* allocateBaz(){
> >> > Baz* baz = malloc(sizeof(Baz));
> >> > Bar* bar = malloc(sizeof(Bar));
> >> > Foo* foo = malloc(sizeof(Foo));
> >> > baz->f = foo;
> >> > baz->b = bar;
> >> > return baz;
> >> > }
> >> > */
> >> > import "C"
> >> > //-------------------------------------------------
> >> >
> >> > //main.go
> >> > package main/*
> >> > #include<c_header.h>
> >> > extern Baz* allocateBaz();
> >> > */
> >> > import "C"
> >> > import "unsafe"
> >> > type GoBaz C.struct_Baz
> >> > type GoBar C.struct_Bar
> >> > type GoFoo C.struct_Foo
> >> > func main() {
> >> > baz_ptr := (*GoBaz)(unsafe.Pointer(C.allocateBaz()))
> >> > bar_ptr := (*GoBar)(unsafe.Pointer(baz_ptr.b))
> >> > foo_ptr := (*GoFoo)(unsafe.Pointer(foo_ptr.f))
> >> > }
> >> > //--------------------------------
> >>
> >>
> >> Interesting. I think that has to do with the fact that you are using
> >> two different Go files that both #include <c_header.h>. <c_header.h>
> >> uses typedef to define anonymous structs. The fact that the header is
> >> being included twice in the same package seems to be causing cgo to
> >> generate two different Go structs, one for each .go file. And then it
> >> can't figure out the definition of the Go struct, so you get this
> >> error.
> >>
> >> This is probably a bug in cgo, so feel free to file an issue at
> >> https://golang.org/issue.
> >>
> >> You can probably make progress by combining the .go files so that you
> >> only have a single import "C" with a #include <c_header.h>.
> >>
> >> Ian
> >
> > --
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> .
>
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