(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?
Thanks!
Mark
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