2022-06-13：golang中，[]byte和结构体如何相互转换？

package main

import (
  "bytes"
  "encoding/binary"
  "fmt"
  "unsafe"
)

type T struct {
  A int64
  B float64
}

func main() {
  if true {
    fmt.Println("切片和结构体内存不共用")
    // Create a struct and write it.
    t := T{A: 1, B: 3.14}
    buf := &bytes.Buffer{}
    err := binary.Write(buf, binary.LittleEndian, t)
    if err != nil {
      panic(err)
    }
    fmt.Println(buf.Bytes())

    // Read into an empty struct.
    t = T{}
    err = binary.Read(buf, binary.LittleEndian, &t)
    if err != nil {
      panic(err)
    }
    fmt.Printf("%x %f\r\n", t.A, t.B)
  }
  fmt.Println("-------------------------")
  if true {
    fmt.Println("切片和结构体内存共用")
    t1 := T{A: 1, B: 3.14}
    fmt.Println("原结构体：", t1)
    sm1 := SimulatedSlice{
      Addr: unsafe.Pointer(&t1),
      Len:  int(unsafe.Sizeof(t1)),
      Cap:  int(unsafe.Sizeof(t1)),
    }
    bytes1 := *(*[]byte)(unsafe.Pointer(&sm1))
    bytes1[0] = 2
    fmt.Println("修改切片，结构体变成：", t1)
    fmt.Println(bytes1)
    fmt.Println("")

    bytes2 := []byte{1, 3, 0, 0, 0, 0, 0, 0, 0, 31, 133, 235, 81, 184, 30, 9, 64}
    fmt.Println("原切片：", bytes2)
    t2 := (*T)(unsafe.Pointer(&bytes2[1]))
    t2.A = 4
    fmt.Println("以为会有内存对齐问题，实际上没问题。修改结构体，切片变成：", bytes2)
    fmt.Println(t2)
    fmt.Println("地址不是8的整数倍：", uintptr(unsafe.Pointer(&bytes2[1])))
    fmt.Println("地址不是8的整数倍：", uintptr(unsafe.Pointer(t2)))
    fmt.Println("严格将首地址需要是8的倍数。")
    fmt.Println("一般也没事。")
    fmt.Println("但有些场合需要严格遵守这个规则，否则会出现问题。")
    fmt.Println("虽然这里没出现问题，但是结构体首地址最好是8的整数倍。不过很多CPU帮你解决了。MIPS会直接崩溃。")
    fmt.Println("这里没出现问题，那是因为很多CPU帮你解决了。MIPS会直接崩溃。这个答案来自qq群友。我并没有去验证。")

  }
}

type SimulatedSlice struct {
  Addr unsafe.Pointer
  Len  int
  Cap  int
}