Passing arrays of structs between Go and C

README.md

1. Put cinterface.go, cinterface.c and test.h in ~/go/src/cinterface/
2. Then call go build -buildmode=c-archive cinterface, this will produce cinterface.a and cinterface.h in current directory
3. Put main.c and test.h in current directory and call gcc -o main -I. cinterface.a main.c, this will produce final binary

cinterface.c

#include <stdlib.h>
#include "test.h"

struct example * getArray(int size) {
	struct example *result = malloc(sizeof(struct example)*size);
	return result;
}

void putData(struct example * array, int position, unsigned long long number, char *str) {
	struct example *element = &array[position];
	element->number = number;
	element->str = str;
}

cinterface.go

package main

/*
#include <stdlib.h>
#include "test.h"
 */
import "C"

type testing struct {
	number uint64
	str string
}

var data = []testing{
	{number:1, str:"one"},
	{number:2, str:"two"},
	{number:3, str:"three"},
}

var ptr *C.struct_example
var ptrSize C.int

func main() {
	// do nothing
}

//export Prepare
func Prepare() {
	ptrSize = C.int(len(data))
	ptr = C.getArray(ptrSize)
	for i:=0; i<len(data);i++ {
		C.putData(ptr,C.int(i), C.ulonglong(data[i].number), C.CString(data[i].str))
	}
}

//export GoGetArray
func GoGetArray() *C.struct_example {
	return ptr
}

//export GoGetArrayLength
func GoGetArrayLength() C.int {
	return ptrSize
}

main.c

#include <stdio.h>
#include "cinterface.h"

int main() {
	Prepare();
	struct example *ptr = (struct example *)GoGetArray();
	int ptr_size = GoGetArrayLength();
	printf("Number of elements: %d\n", ptr_size);
	for(int i = 0; i < ptr_size; i++) {
		struct example e = ptr[i];
		printf("Element %d: number=%llu, str=%s\n", i, e.number, e.str);
	}
	return 0;
}

test.h

struct example
{
	unsigned long long number;
	char *str;
};

struct example * getArray(int size);

void putData(struct example * array, int position, unsigned long long number, char *str);