golang 获得一个结构体的字节大小

golang 的内存占用是如何构成的呢?

unsafe.SizeOf()

转载：如何在Go中获取变量的内存大小？--CSDN问答

如果传递一个未初始化的变量，unsafe.Sizeof()与reflect.Type.Size()将只返回传递的变量的类型的大小，并不递归地遍历数据结构并增加所指向变量的大小。

切片是一个相对简单的结构体struct：reflect.SliceHeader，因为我们知道切片是引用一个备份的数组（或字符串——byte数组），我们可以简单地手动计算它的大小：

sliceint := make([]int32, 1000) //指向元素类型为int32的1000个元素的数组的切片
fmt.Println("Size of []int32:", unsafe.Sizeof(sliceint)) //24
fmt.Println("Size of [1000]int32:", unsafe.Sizeof([1000]int32{})) //4000
fmt.Println("Real size of s:", unsafe.Sizeof(sliceint)+unsafe.Sizeof([1000]int32{})) //4024
输出：

Size of []int32: 24
Size of [1000]int32: 4000
Real size of s: 4024
也就是创建一个相同类型的初始化过的切片，并

func GetGoVarSize(val any) (sumSize int) {
	vl := reflect.ValueOf(val)
	tp := reflect.TypeOf(val)
	//tp.Size() + vl.Kind()
	switch vl.Kind() {
	case reflect.Bool, reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64, reflect.Uint, reflect.Uint8,
		reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr, reflect.Float32, reflect.Float64, reflect.Complex64,
		reflect.Complex128:
		return int(tp.Size()) //unsafe.Sizeof(val)
	case reflect.Map:
		forSize := int(tp.Size())
		for _, i := range vl.MapKeys() {
			forSize += GetGoVarSize(i.Interface()) + GetGoVarSize(vl.MapIndex(i).Interface())
		}
		return forSize
	case reflect.Array, reflect.Slice:
		forSize := int(tp.Size())
		for i := 0; i < vl.Len(); i++ {
			forSize += GetGoVarSize(vl.Index(i).Interface())
		}
		return forSize
		//return int(tp.Size()) + vl.Len()*GetGoVarSize(vl.Elem().Interface())//array and slice , not have Elem()
	case reflect.Chan:
		//请注意，尝试获取channel元素类型的操作（即varType.Elem()）是不允许的，因为这将导致运行时的panic。在Go中，你不能通过反射来获取channel的元素类型。
		forSize := int(tp.Size())
		for i := 0; i < vl.Len(); i++ {
			forSize += 0
		}
		return forSize
	case reflect.Func:
		return int(tp.Size())
	case reflect.Interface:
		fallthrough
	case reflect.Pointer:
		forSize := int(tp.Size())
		if vl.IsNil() {
			return forSize
		}
		return forSize + GetGoVarSize(vl.Elem().Interface())
	case reflect.String:
		forSize := int(tp.Size())
		for i := 0; i < vl.Len(); i++ {
			forSize += GetGoVarSize(vl.Index(i).Interface())
		}
		return forSize
	case reflect.Struct:
		forSize := int(tp.Size())
		for i := 0; i < vl.NumField(); i++ {
			tpField := tp.Field(i)
			vlField := vl.Field(i)
			if tp.Name() == "Time" && tp.PkgPath() == "time" {
				_ = &time.Time{}
				//forSize += 8*2 + GetGoVarSize(time.Location{})
				//forSize += 8*2 + (16 + 5) + (24 + (8 + 3) + (8 + 1)) + (24 + (8 + 1 + 2)) + (16 + 0) + 8 + 8 + (8 + (3 + 8 + 1))
				forSize += 24 //time.Time{} 基本都是空数据,就用这个; 有 time.Local的才会用到上面的这个.
				continue
			}
			if !tpField.IsExported() {
				s := int(vlField.Type().Size()) //int(tpField.Type.Size())
				forSize += s
				log.Printf("Struct (%T)'s field(%v) not IsExported() string:%v, theSize=%v tp=%v vl=%v\n", val, i, vlField.String(), s, tpField, vlField)

				//TODO 不可导出字段,应该可以通过 unsafe 获取数据的. 不处理这个问题,无法获得真实的大小的.
				//var tp = reflect.New(tpField.Type)
				//tp.SetPointer(unsafe.Pointer(vlField.UnsafePointer()))
				//forSize += GetGoVarSize(tp.Interface())

				continue
			}
			if !vlField.CanInterface() {
				s := int(vlField.Type().Size())
				forSize += s
				log.Printf("Struct (%T)'s field(%v) cannot string:%v theSize use :%v\n", val, i, vlField.String(), s)
				continue
			}

			switch vlField.Kind() {
			case reflect.Chan, reflect.Func, reflect.Map, reflect.Pointer, reflect.UnsafePointer,
				reflect.Interface, reflect.Slice:
				if vlField.IsNil() {
					forSize += int(vlField.Type().Size())
					continue
				}
			}
			forSize += GetGoVarSize(vlField.Interface())
		}
		return forSize
	case reflect.UnsafePointer:
		forSize := int(tp.Size())
		return forSize
	default:
		//return 0
		panic(fmt.Errorf(" %T Not support Kind %v", val, vl.Kind()))
	}
	return 0
}