Go study notes - pointer

Go study notes - pointer

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1. The basis of pointers

The Go language retains the use of pointers like the C language, but Go's pointers are safe pointers and cannot be used for offset and operations.

First of all, let's distinguish between pointer variables and ordinary variables

• Pointer variable: define a space to store the address of the value
• Ordinary variable: define a space to directly store the value itself

Followed by the pointer type and pointer value :

• Pointer type: *int, *stringetc., each corresponding data type can be used as a pointer type.

Similar to the C language, the Go language also uses &and *to manipulate variables about pointers

• &: Represents the address symbol, which is used to obtain the address of a variable and store it in another variable
• *: Represents the accessor, which is used to obtain the value from the variable at the storage address

func mainPointer() {
	var a int
	a = 100    //此时a是一个普通的变量
	fmt.Printf("%d\n", a)  //a存储一个值
    b = &a     //b存放的是a的地址，此时b是一个指针变量
	fmt.Printf("%p\n", b) //b存储一个地址
    fmt.Printf("%p\n", &a) //&a存储一个地址
	fmt.Println(*&a)       //*&a存储一个值
	//fmt.Printf("%x\n",&a)

	//指针变量的定义，用来存储变量的地址
	var p *int //定义指针变量
    			//*int属于指针类型
	//定义指针变量就是定义一个空间用来存储地址
	p = &a //把变量a的地址赋值给变量p
	fmt.Println(p)   //此时p存储的是a的地址
	*p = 80          //将p对应的地址赋值为80
	fmt.Printf("a=%d,p=%v\n", a, p)
	fmt.Printf("a=%d,p=%v", a, *p)

}

2. Expansion of pointers

• A null pointer is a pointer variable that does not take an address. The default value isnil

	//空指针
	var q *int
	fmt.Println(q)
	//指针的空值为nil，系统中默认的值

• new()Function to create an address space of the specified type size

	var p *int
	p = new(int)
	*p = 57
	fmt.Println(p, *p)

• pointers as function arguments

package main
import "fmt"
func Swap(num1,num2 *int){
    
    
	*num1,*num2 = *num2,*num1
	fmt.Println(*num1,*num2)
}
func main() {
    
    
	a := 10
	b := 20
	Swap(&a,&b)
	//普通变量在函数中传递是值传递
	//指针变量作为函数参数是地址传递
	fmt.Println(a,b)
}