Go defer and recover simple notes

defer Mechanism

go Of defer The mechanism is used to release some resources before the end of the function , Multiple... Can be defined in the function defer, After definition, execute first , Advanced chef , It's a stack . When the function wants to return when , I will put return Copy the value of , And then do it one by one defer Code ( stay defer Change in return Variables of no longer affect return Value ), Finally, return to the copied return value

recover Mechanism

recover Used to capture the occurrence of the current function and its called sub functions panic error , Let the current program continue , If the whole program is not captured, it will exit .recover Only written in defer Only valid in code blocks

The Works of Liezi ：

package main

import "fmt"

func test1() int {
	defer func() {
		err:=recover()
		if err != nil {
			fmt.Println("panic:",err)
		}
	}()
	test2()
	fmt.Println(" You can't see me ")
	return 1
}

func test2() {
	var p *int
	*p = 1//runtime panic
}

func main() {
	fmt.Println(" Before execution ")
	ret:=test1()
	fmt.Println("return:",ret)
	fmt.Println(" After execution ")
}

Execution results ：

 Before execution 
panic: runtime error: invalid memory address or nil pointer dereference
return: 0
 After execution 

analysis ： According to the running results of the program , Happen when panic, Later code will no longer be executed , until recover after . In this column test1() Caught in panic,test1 The following code is no longer executed ,test1() Will end and return a zero value of the return value type ,test1 The return value type of is int, So back 0, go back to main Continue execution in function