On Fri, Apr 17, 2020 at 7:34 AM mark mellar <radiatorf...@gmail.com> wrote: > > (Cross posting with SO > https://stackoverflow.com/questions/61258160/swig-generated-go-wrapper-mishandling-pointers-to-pointers-to-structs) > > Hi folks, > > We're integrating a Go program with a 3rd party C api, but are getting some > odd results when working with pointers to pointers to structs. A model of the > header file looks a bit like this... > > //mytest.h > > typedef struct Books { > char title[50]; > char author[50]; > char subject[100]; > int book_id; > } > > Book; extern void initbook(Book** b); > > With a model implementation like this... > > //mytest.c > #include <stdlib.h> > #include <string.h> > #include <stdio.h> > > typedef struct Books { > char title[50]; > char author[50]; > char subject[100]; > int book_id; > } Book; > > void initbook(Book** b){ *b = malloc(sizeof(Book)); > strcpy( (*b)->title, "A Book Title"); > } > > We've tried wrapping the API with a very simple SWIG file which looks like > this... > > %module mytest %{ > #include "./mytest.h" > %} > %include "./mytest.h" > > And call it from a Go main function like this... > > //main.go > > package main > import "fmt" > import "mytest" > func main() { > bookPtr := mytest.NewBook() > mytest.Initbook(bookPtr) > fmt.Printf("title: '%s'\n", bookPtr.GetTitle()) > } > > However, we've found when we run this we the value being returned from > GetTitle() is garbled.... > > > go run ../main.go > title: '??' > > Digging in to the generated C code we found that editing the Book constructor > to return Book** rather than Book*, and then modifying the GetTitle function > to receive a Book** instead of Book* things started working as expected. > > Any hints on how we might configure SWIG to generate a version of the code > which works for us. without us having to hack what it generates?
Since this is a C API, I suggest that you use cgo. https://blog.golang.org/cgo. If you want to use SWIG, you'll likely need to use directives like %gotype to teach SWIG how the C type should be represented in Go. It seems clear that SWIG is getting confused, as from what you wrote above it seems that the Go code ought to be mytest.Initbook(&bookPtr). Ian -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/golang-nuts/CAOyqgcUnDW9ZTZZnsjXN9kjLzTYb4weAji%2BE4ne%3DCsOiS2NT6Q%40mail.gmail.com.
