example_test.go

package ffi_test

import (
	"fmt"
	"math"
	"unsafe"

	"github.com/jupiterrider/ffi"
)

func ExamplePrepClosureLoc() {

	// This example recreates a well-known math function and then calls it.

	var sin unsafe.Pointer
	closure := ffi.ClosureAlloc(unsafe.Sizeof(ffi.Closure{}), &sin)
	defer ffi.ClosureFree(closure)

	fun := ffi.NewCallback(func(cif *ffi.Cif, ret unsafe.Pointer, args *unsafe.Pointer, userData unsafe.Pointer) uintptr {
		arg := unsafe.Slice(args, cif.NArgs)[0]
		sine := math.Sin(*(*float64)(arg))
		*(*float64)(ret) = sine
		return 0
	})

	var cif ffi.Cif
	if status := ffi.PrepCif(&cif, ffi.DefaultAbi, 1, &ffi.TypeDouble, &ffi.TypeDouble); status != ffi.OK {
		panic(status)
	}

	// sin becomes a C function pointer with the following signature:
	// double sin(double x);
	if status := ffi.PrepClosureLoc(closure, &cif, fun, nil, sin); status != ffi.OK {
		panic(status)
	}

	sine, x := 0.0, 1.0
	ffi.Call(&cif, uintptr(sin), unsafe.Pointer(&sine), unsafe.Pointer(&x))
	fmt.Println(sine)
	// Output: 0.8414709848078965
}

func ExampleGetStructOffsets() {
	type example struct {
		b  byte
		f  float32
		b2 byte
		i  int32
	}

	exampleType := ffi.NewType(&ffi.TypeUint8, &ffi.TypeFloat, &ffi.TypeUint8, &ffi.TypeSint32)

	var offsets [4]uint64

	if status := ffi.GetStructOffsets(ffi.DefaultAbi, &exampleType, &offsets[0]); status != ffi.OK {
		panic(status)
	}

	var e example
	fmt.Println(uint64(unsafe.Sizeof(e)) == exampleType.Size)
	fmt.Println(uint64(unsafe.Offsetof(e.b)) == offsets[0])
	fmt.Println(uint64(unsafe.Offsetof(e.f)) == offsets[1])
	fmt.Println(uint64(unsafe.Offsetof(e.b2)) == offsets[2])
	fmt.Println(uint64(unsafe.Offsetof(e.i)) == offsets[3])
	// Output:
	// true
	// true
	// true
	// true
	// true
}