英文:
Golang: Assigning a value to struct member that is a pointer
问题
我正在尝试为一个指针类型的结构成员赋值，但在运行时出现了"panic: runtime error: invalid memory address or nil pointer dereference"的错误。
package main
import (
"fmt"
"strconv"
)
// Test
type stctTest struct {
blTest *bool
}
func main() {
var strctTest stctTest
*strctTest.blTest = false
fmt.Println("Test is " + strconv.FormatBool(*strctTest.blTest))
}
这个运行时错误似乎是由于*strctTest.blTest = false这行代码的赋值引起的，但是为什么会出错呢？我该如何将其设置为false呢？
英文:
I'm trying to assign a value to a struct member that is a pointer, but it gives "panic: runtime error: invalid memory address or nil pointer dereference" at runtime...
package main
import (
"fmt"
"strconv"
)
// Test
type stctTest struct {
blTest *bool
}
func main() {
var strctTest stctTest
*strctTest.blTest = false
fmt.Println("Test is " + strconv.FormatBool(*strctTest.blTest))
}
The runtime error seems to come from the assignment of the value with *strctTest.blTest = false , but why? How do I set it to false?
答案1
得分: 17
为什么会出错？因为指针只是指向一个位置，它本身并不创建任何要指向的内容。你需要自己创建。
如何将其设置为false？这取决于你为什么将其设置为指针。
如果每个副本都应该指向相同的布尔值，那么应该在创建函数中为其分配一些空间。
func NewStruct() *strctTest {
bl := true
return &strctTest{
blTest: &bl,
}
}
如果用户应该将其指向自己的布尔值，那么在创建对象时应该手动设置。
func main() {
myBool := false
stctTest := strctTest{
blTest: &myBool,
}
fmt.Println("Test is " + strconv.FormatBool(*strctTest.blTest))
}
英文:
Why is it an error? Because a pointer only points. It doesn't create anything to point AT. You need to do that.
How to set it to false? This all depends on WHY you made it a pointer.
Is every copy of this supposed to point to the same bool? Then it should be allocated some space in a creation function.
func NewStruct() *strctTest {
bl := true
return &strctTest{
blTest: &bl,
}
}
Is the user supposed to point it at a boolean of his own? Then it should be set manually when creating the object.
func main() {
myBool := false
stctTest := strctTest{
blTest: &myBool
}
fmt.Println("Test is " + strconv.FormatBool(*strctTest.blTest))
}
答案2
得分: 2
另一种思考方式是布尔类型的零值为false。
这个不太清楚，但还有另一种方法可以实现。
https://play.golang.org/p/REbnJumcFi
我建议使用一个New()函数，返回一个初始化的结构体类型的引用。
英文:
Another way you can think of it is the zero value of a boolean is false.
This is not as clear but another way to do it.
https://play.golang.org/p/REbnJumcFi
I would recommend a New() func that returns a reference to a initialized struct type.
答案3
得分: 2
你也可以这样做：
package main
import (
"fmt"
"strconv"
)
// 测试
type stctTest struct {
blTest *bool
}
func main() {
strctTest := stctTest{
blTest: &[]bool{true}[0],
}
fmt.Println("测试结果为：" + strconv.FormatBool(*strctTest.blTest))
}
链接：https://play.golang.org/p/OWSosQhrUql
英文:
You could also do something like:
package main
import (
"fmt"
"strconv"
)
// Test
type stctTest struct {
blTest *bool
}
func main() {
strctTest := stctTest{
blTest: &[]bool{true}[0],
}
fmt.Println("Test is " + strconv.FormatBool(*strctTest.blTest))
}
答案4
得分: 0
以下是翻译好的内容：
根据JT的回答，我也建议使用new函数，如下所示：
package main
import (
"fmt"
"strconv"
)
// Test
type stctTest struct {
blTest *bool
}
func main() {
strctTest := &stctTest{
blTest: new(bool),
}
*strctTest.blTest = true
fmt.Println("Test is " + strconv.FormatBool(*strctTest.blTest))
}
在使用new()初始化内存之后，您可以直接给解引用的指针赋值。这样，您就不需要使用另一个变量来获取地址。
链接：https://go.dev/play/p/BmekoTalQVh
英文:
Following up on JTs Answer, I also would recommend using the new function as such:
package main
import (
"fmt"
"strconv"
)
// Test
type stctTest struct {
blTest *bool
}
func main() {
strctTest := &stctTest{
blTest: new(bool),
}
*strctTest.blTest = true
fmt.Println("Test is " + strconv.FormatBool(*strctTest.blTest))
}
After initializing the memory with new(), you can directly assign a value to the de-referenced pointer. This way you do not need to use another variable to get the address from.
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