Go language foundation ----- 09 ----- exception handling (error, panic, recover)

1 error

1.1 error About
error It usually deals with some relatively low-level errors , It will not cause program interruption or downtime . Here is go Source code error Related content of ：

//  Interface definition 
type error interface{
    
	Error() string
}

package errors

//  Wrong structure definition 
type errorString struct{
    
	text string
}

//  The errorString Implementation of the method of structure 
func (e *errorString)Error() string{
    
	return e.text
}

//  Finally, you can get a through this function errorString structure , So that you can call Error Method .
func New(text string) error{
    
	return &errorString(text)
}

For example, simply use two error functions of the standard library ：

package main

import (
	"errors"
	"fmt"
)

func main(){
    

	err1 := fmt.Errorf("%s", "this is a Errorf")
	fmt.Println("err1: ", err1)

	err2 := errors.New("this New error")
	fmt.Println("err2: ", err2)
}

1.2 error Common usage

package main

import (
	"errors"
	"fmt"
)

// error  by nil Explain normal , Otherwise, the report will be wrong , Information from errors.New obtain 
func MyDiv(a, b int) (result int, err error){
    
	err = nil
	if b == 0 {
    
		err = errors.New(" The denominator cannot be 0")
	}else{
    
		result = a/b
	}
	return 	//  Equivalent to  return result, err
}

func main(){
    

	ret, err := MyDiv(2, 2)
	if err == nil{
    
		fmt.Println("ret = ", ret)
	}else{
    
		fmt.Println(" Expression has illegal value , err: ", err)
	}

	ret, err = MyDiv(2, 0)
	if err == nil{
    
		fmt.Println("ret = ", ret)
	}else{
    
		fmt.Println(" Expression has illegal value , err: ", err)
	}
}

2 panic

• 1）panic It is usually called when a fatal error occurs , For example, the array is out of bounds , Null pointer, etc , Of course, we can also manually call panic() Function to trigger . similar C Linguistic assert() Assertion function .

2.1 Show manual call panic

package main

import "fmt"

func testa(){
    
	fmt.Println("aaaaaaaaaaaaaa")
}

func testb(){
    
	//fmt.Println("bbbbbbbbbbbbbb")
	//  Manual call panic() Will trigger an assertion 
	panic("manual triggered assertions, the program breaks")
}

func testc(){
    
	fmt.Println("ccccccccccccccc")
}

func main(){
    
	testa()
	testb()
	testc()
}

The relevant errors are as follows ：

2.2 Array out of bounds, resulting in panic

package main

import "fmt"

func testa(){
    
	fmt.Println("aaaaaaaaaaaaaa")
}

func testb(index int){
    
	//fmt.Println("bbbbbbbbbbbbbb")
	//  Manual call panic() Will trigger an assertion 
	// panic("manual triggered assertions, the program breaks")

	//  Array out of bounds, resulting in panic Assertion 
	var x [10]int
	fmt.Println("x: ", x[index])
}

func testc(){
    
	fmt.Println("ccccccccccccccc")
}

func main(){
    
	testa()
	testb(10)	//  Array out of bounds triggers assertion 
	testc()
}

3 recover function

Happen when panic When it's wrong , It interrupts the program , But sometimes we don't want the program to break , We can use recover Function to capture this interrupt .
But notice ：

• 1）recover() Only in defer The function called is valid . When defer, And this function happens panic error , Then the error will be caught , The program will return to normal .

for example ：

package main

import "fmt"

func testa(){
    
	fmt.Println("aaaaaaaaaaaaaa")
}

func testb(index int){
    
	//fmt.Println("bbbbbbbbbbbbbb")
	//  Manual call panic() Will trigger an assertion 
	// panic("manual triggered assertions, the program breaks")

	//  Set up recover
	defer func() {
    
		if err := recover(); err != nil{
    
			//fmt.Println("errInfo: ", recover())//  Don't call... Again recover() As information , Because the call is normal at this time ,
			// Because there are no mistakes , The error is already in if Caught in 
			fmt.Println("errInfo: ", err)
		}
	}()

	//  Array out of bounds, resulting in panic Assertion 
	var x [10]int
	fmt.Println("x: ", x[index])
}

func testc(){
    
	fmt.Println("ccccccccccccccc")
}

func main(){
    
	testa()
	testb(10)	//  Array out of bounds triggers assertion 
	testc()
}