指針在GO中的零值是多少？

在Go中，指針的零值是nil，表示未指向任何有效內存地址。 1. 聲明未初始化的指針時，默認值為nil，不可直接解引用，否則引發運行時panic。 2. 安全使用指針前應通過new()或取址操作賦予有效地址。 3. 結構體或集合中的指針字段默認為nil，可用於區分未設置與零值的情況。 4. 解引用前務必檢查指針是否為nil以避免程序崩潰。

In Go, the zero value of a pointer is nil .

That's straightforward, but there's a bit more to understand about how pointers and their zero values behave in different contexts.

What does a pointer's zero value mean?

When you declare a pointer variable without explicitly assigning it a value, Go initializes it with its zero value , which is nil . This means the pointer doesn't point to any valid memory address yet.

For example:

 var p *int
fmt.Println(p) // Output: <nil>

This behavior is consistent across all pointer types — whether it's *int , *string , or a pointer to a struct. The key takeaway is that a nil pointer isn't pointing to anything useful, and trying to dereference it will cause a runtime panic.

How do you safely use a pointer after declaration?

Before using a pointer (especially dereferencing it), you should always make sure it points to a valid value. A common pattern is to assign the result of new() or take the address of an existing variable.

Examples:

 var p *int
p = new(int) // now p points to a valid int with zero value 0
*p = 10

// Or
var x = 5
p = &x

If you skip this step and try:

 var p *int
fmt.Println(*p) // This will crash your program

You'll get a runtime panic like: invalid memory address or nil pointer dereference .

So, a good practice is to always check if a pointer is nil before dereferencing it.

When does a pointer stay as nil in real code?

Pointers often start out as nil when they're part of structs, slices, or maps that are initialized without specific values.

Example:

 type User struct {
    Age *int
}

user := User{}
fmt.Println(user.Age) // <nil>

Here, the Age field is a pointer and remains nil unless explicitly assigned. This can be useful for distinguishing between a zero value and an unset value — for instance, knowing whether Age was set to 0 or just never provided at all.

In such cases, checking if age != nil becomes important before using the value.

Summary

• The zero value of any pointer type in Go is nil .
• Dereferencing a nil pointer causes a panic.
• Always initialize or assign a valid address before using a pointer.
• Pointers in structs or collections start as nil unless explicitly set.

基本上就這些。

以上是指針在GO中的零值是多少？的詳細內容。更多資訊請關注PHP中文網其他相關文章！