我在Go中管理结构有一些问题。我有复杂的结构和两个基于该结构的变量 - “previous”和“current”。我正在尝试从tarfile中读取数据,进行一些计算并用current替换之前的数据。但是在我读到当前的下一次阅读迭代时,在我看来,“先前”的内容被覆盖,两个变量都变得相同。结构定义如下:
type Mystruct struct {
Data [][]sql.NullString
Rnames []string
Nsize int
Msize int
Namemaxlen map[string]int
Valid bool
Err error
}
变量不是指针。复制作为直接赋值执行:previous = current。
tr := tar.NewReader(f)
var prev, curr Mystruct
for {
hdr, err := tr.Next()
if err == io.EOF {
break
} else if err != nil {
log.Panicln(err)
}
data := make([]byte, hdr.Size)
if _, err := io.ReadFull(tr, data); err != nil {
log.Panicln(err)
}
if err = json.Unmarshal(data, &curr); err != nil {
log.Panicln(err)
}
if prev.Valid != true {
prev = curr
continue
}
// other computations here
prev = curr
}
我哪里错了?提前致谢。
问题是你的struct包含基本上是指向内存的指针。复制这些指针意味着您的副本指向SAME内存作为原始内容,因此它们共享切片值。改变一个会改变另一个。
这是a small example来说明问题:
package main
import "fmt"
type s struct {
a int
slice []int
}
func main() {
// create the original thing
prev := s{
a: 5,
slice: []int{1, 2, 3},
}
// copy the thing into cur
cur := prev
// now change cur, changing a will change only cur.a because integers are
// really copied
cur.a = 6
// changing the copied slice will actually change the original as well
// because copying a slice basically copies the pointer to memory and the
// copy points to the same underlying memory area as the original
cur.slice[0] = 999
// printing both, we can see that the int a was changed only in the copy but
// the slice has changed in both variables, because it references the same
// memory
fmt.Println(prev)
fmt.Println(cur)
}