Helsinki Gophers May 2016 meetup Cgo code examples

README.md

Cgo Code examples

Helsinki Gophers May 2016 meetup

Building and running

go build -o demo .
./demo

Presentation

You can find the presentation at mumakil.fi/p/hki-gophers-may-2016.

go-libphonenumber

You can find the go-libphonenumber project in GitHub at Applifier/go-libphonenumber.

allocate_and_free.go

package main

// #import <stdio.h>
// #import <stdlib.h>
import "C"
import "unsafe"

// AllocateAndFree allocates a C string, prints it and frees it
func AllocateAndFree() {
	cStr := C.CString("I'm a string, yay!")
	defer C.free(unsafe.Pointer(cStr))
	C.puts(cStr)
}

hello_world.c

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

void hello_world() {
  printf("Hello world!\n");
}

hello_world.go

package main

// #include "hello_world.h"
import "C"

// HelloWorld prints out hello world using C code
func HelloWorld() {
	C.hello_world()
	// Prints "Hello world!"
}

hello_world.h

void hello_world();

main.go

package main

import (
	"fmt"
)

func main() {
	fmt.Println("Example 1: hello world using C")
	HelloWorld()

	fmt.Println("Example 2: call C namespace")
	PrintSquared(8)

	fmt.Println("Example 3: allocate and free")
	AllocateAndFree()
}

print_squared.go

package main

// #include <math.h>
import "C"
import "fmt"

// PrintSquared squares the number using C math
func PrintSquared(f float64) {
	n, _ := C.pow(C.double(f), C.double(2))
	fmt.Printf("%f squared is %f\n", f, float64(n))
}