How to use pointers in Go?

Pointers are an important concept in the Go language and are often used for indirect access and modification of variables. Using pointers can improve program efficiency and flexibility, but if you don't pay attention to the use of pointers, it may cause some errors and problems. This article will introduce the basic concepts and usage of pointers in Go language, and explain it with code examples.

1. The concept and definition of pointers

In Go language, a pointer is a variable that stores the memory address of a variable. In other words, a pointer is a variable whose value is the address of another variable. The variable pointed to by the pointer can be any type of variable, including basic types and composite types.

Pointer type variables need to be declared with "*" to indicate that this is a pointer variable, for example:

var p *int  //声明一个整型指针变量p

In the above code, p is a pointer to an integer variable variable, but p does not currently point to any variable. If you need to make p point to an integer variable, you can use the "&" address symbol to get the address of the variable, and then assign it to p. For example:

var a int = 10
p = &a   //a的地址赋值给p

In the above code, p points to the variable a Address, you can access the value of the variable pointed to by p through the dereference symbol "*", for example:

fmt.Println(*p)  //输出p所指向的变量a的值，即10

2. Operation and use of pointers

1. Transfer of pointers

In Go language, pointers can be passed as function parameters. The operation of pointer variables in the function will directly affect the value of the corresponding variable outside the function. For example:

func changeValue(p *int) {
    *p = 20  //通过解引用符号来修改p所指向的变量的值
}

func main() {
    var a int = 10
    var p *int = &a
    changeValue(p)  //传递指针p给函数
    fmt.Println(a)  //输出修改后的a的值，即20
}

In the above code, the pointer p is passed to the function changeValue, and the point pointed to by p is modified in the function. The value of the variable ultimately affects the value of the variable a outside the function. Because the pointer passes the address in the program, the value of the variable can be modified in the function through the pointer, affecting the external variables of the function.

2. Comparison of pointers

In Go language, you can use the "==" and "!=" operators to compare pointers. If the addresses of two pointers pointing to the same variable are the same, then they are equal, for example:

var a int = 10
var p1 *int = &a
var p2 *int = &a
fmt.Println(p1 == p2)  //输出true，因为p1和p2都指向变量a的地址

In the above code, p1 and p2 both point to the address of variable a, so they are equal.

3. NULL value of pointer

In Go language, a pointer variable can be assigned a null value nil, which means that the pointer does not point to any variable, for example:

var p *int = nil

The above In the code, p is an integer pointer variable. Assigning a value of nil means that p does not point to any variable. If you attempt to dereference a null pointer in your program, a runtime error will result.

4. Slicing of pointers

In Go language, pointers can be stored and operated as elements of slices. For example:

var a int = 10
var b int = 20
var p1 *int = &a
var p2 *int = &b
var slice []*int = []*int{p1, p2}  //声明指向整型指针变量的切片
fmt.Println(*slice[0])  //输出p1指向的变量的值，即10
fmt.Println(*slice[1])  //输出p2指向的变量的值，即20

In the above code, a slice pointing to an integer pointer variable is declared, the variables p1 and p2 are stored in the slice, and the values ​​of the variables they point to can be accessed through the slice elements.

3. Summary

This article introduces the concept, definition and basic operations of pointers in Go language. Pointers are a powerful feature that can improve the efficiency and flexibility of programs, but you also need to pay attention to the use of pointers to prevent problems such as pointer errors and dangling pointers. In the Go language, it is recommended to avoid using pointers to operate composite data types such as slicing and mapping, which can improve the safety and readability of the code.

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