踩坑记录
for循环中地址问题
遍历有缓冲的chan, 赋值结果到指针数组
测试代码: chan2Slice
缓冲chan通常用作多协程的结果返回
- 异常代码
// 循环读取channel，取地址append到数组
type ChanStruct struct {
Num int
Data string
}
func main() {
// 定义chan
ptrChan := make(chan ChanStruct, 10)
for i:= 1;i < 10;i++ {
cs := ChanStruct {
Num: i,
Data: strconv.Itoa(i),
}
ptrChan <- cs
}
close(ptrChan)
var csList []*ChanStruct
// 从chan取数据，放入csList中
for c := range ptrChan {
csList = append(csList, &c)
}
for _, cs := range csList {
fmt.Printf("cs: %d, %s\n", cs.Num, cs.Data)
}
}
- 输出结果
结果不符合预期，新数组中所有元素都是同一个地址
cs: 0xc000086000, 9, 9
cs: 0xc000086000, 9, 9
cs: 0xc000086000, 9, 9
...
- 正确方式
for循环的局部变量地址是不会变的，如果要赋值地址给别人，需要新生成对象，再取地址
// 循环读取channel，取地址append到数组
type ChanStruct struct {
Num int
Data string
}
func main() {
// 定义chan
ptrChan := make(chan ChanStruct, 10)
for i:= 1;i < 10;i++ {
cs := ChanStruct {
Num: i,
Data: strconv.Itoa(i),
}
ptrChan <- cs
}
close(ptrChan)
var csList []*ChanStruct
// 从chan取数据，放入csList中
for c := range ptrChan {
temp := c
csList = append(csList, &temp)
}
for _, cs := range csList {
fmt.Printf("cs: %d, %s\n", cs.Num, cs.Data)
}
}
遍历指针数组，使用遍历时的临时变量
测试代码: for_with_coroutine
- 错误示例1:
代码片段:
for i, v := range dataList {
go func() {
defer wg.Done()
fmt.Printf("cycle %d time, index addr: %p, data addr: %p, value: %s\n", i, &i, &(v.Data), v.Data)
}()
}
返回:
cycle 4 time, index addr: 0xc000088020, data addr: 0xc000062230, value: value5
cycle 4 time, index addr: 0xc000088020, data addr: 0xc000062230, value: value5
cycle 4 time, index addr: 0xc000088020, data addr: 0xc000062230, value: value5
cycle 4 time, index addr: 0xc000088020, data addr: 0xc000062230, value: value5
cycle 4 time, index addr: 0xc000088020, data addr: 0xc000062230, value: value5
- 正确示例1：
代码片段:
for i, v := range dataList {
go func(index int, elem *Elem) {
defer wg.Done()
fmt.Printf("cycle %d time, index addr: %p, data addr: %p, value: %s\n", index, &index, &(elem.Data), elem.Data)
}(i, v)
}
返回:
cycle 0 time, index addr: 0xc000092010, data addr: 0xc0000621e0, value: value1
cycle 4 time, index addr: 0xc000096020, data addr: 0xc000062230, value: value5
cycle 3 time, index addr: 0xc000096030, data addr: 0xc000062220, value: value4
cycle 1 time, index addr: 0xc000018098, data addr: 0xc0000621f0, value: value2
cycle 2 time, index addr: 0xc000092018, data addr: 0xc000062210, value: value3
- 错误示例2：
代码片段:
for i, v := range dataList {
go DataPrintV3(&wg, &i, v)
}
返回:
cycle 4 time, index addr: 0xc000092028, data addr: 0xc0000621e0, value: value1
cycle 4 time, index addr: 0xc000092028, data addr: 0xc000062230, value: value5
cycle 4 time, index addr: 0xc000092028, data addr: 0xc0000621f0, value: value2
cycle 4 time, index addr: 0xc000092028, data addr: 0xc000062210, value: value3
cycle 4 time, index addr: 0xc000092028, data addr: 0xc000062220, value: value4
- 正确示例2：
代码片段:
for i, v := range dataList {
go DataPrintV4(&wg, i, v)
}
返回:
cycle 4 time, index addr: 0xc000088050, data addr: 0xc000062230, value: value5
cycle 2 time, index addr: 0xc000088060, data addr: 0xc000062210, value: value3
cycle 3 time, index addr: 0xc000088070, data addr: 0xc000062220, value: value4
cycle 0 time, index addr: 0xc000088080, data addr: 0xc0000621e0, value: value1
cycle 1 time, index addr: 0xc0000180b0, data addr: 0xc0000621f0, value: value2
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