cgo samples

cgo-sample.go

package main

/*
#include <string.h>

void write_int(int *len) {
	*len = 10;
}

void write_int_array(int *sizes[]) {
	int stack_sizes[] = {1,2,3};

	// Here is an error!
	// *sizes = stack_sizes;

	memcpy(sizes, stack_sizes, sizeof(int)*3);
}

void write_bytes_array(char **data) {
	char stack_data[] = "asdfg";

	// Here is an error!
	// *data = d;

	memcpy(data, stack_data, sizeof(char)*strlen(stack_data));
}

*/
import "C"

import (
	"fmt"
	"unsafe"
)

func main() {
	// Right. But type casting will be needed.
	var cInt C.int
	C.write_int(&cInt)
	fmt.Println(cInt)

	// Wrong. Works, but here we have actually an undefined befavior because of different int types
	var goInt int
	C.write_int((*C.int)(unsafe.Pointer(&goInt)))
	fmt.Println(goInt)

	// Allocating memory in Go part
	sizes := make([]C.int, 3)
	C.write_int_array((**C.int)(unsafe.Pointer(&sizes[0])))
	fmt.Println(sizes)

	// Allocating memory in Go part
	data := make([]C.char, 5)
	C.write_bytes_array((**C.char)(unsafe.Pointer(&data[0])))
	// Need type casting, output will be bytes array
	fmt.Println(data)
}