go_tooling/dump/slice.go

package main

import (
	"fmt"
	"strings"
	"unsafe"
)

type slice struct {
	arrayPtr uint
	len      uint
	cap      uint
}

func (s slice) Data() []byte {
	var p *byte
	var i uint
	res := make([]byte, s.len)
	for i = 0; i < s.len; i++ {
		p = (*byte)(unsafe.Pointer(uintptr(s.arrayPtr) + uintptr(i)))
		res[i] = *p
	}

	return res
}

func Dump(slicePtr *[]byte) {
	var n uintptr = uintptr(unsafe.Pointer(slicePtr))
	var s *slice = (*slice)(unsafe.Pointer(n))
	fmt.Println(*s)
	fmt.Printf("Len: %d, Cap: %d: Data:\n", s.len, s.cap)
	fmt.Printf("%#v\n", s.Data())
}

func main() {
	var max byte = 13
	a := make([]byte, max, 64)
	var i byte
	for i = 0; i < max; i++ {
		a[i] = '@' + i
	}
	fmt.Println(a, len(a), cap(a))

	Dump(&a)

	var z int
	fmt.Println(unsafe.Sizeof(z))

	r := strings.NewReader("ceci est une chaîne")
	var s []byte

	n, err := r.ReadAt(s, 4)
	fmt.Println("Read: %n (%v): %#v\n", n, err, s)

}