panic defer recover

偏执的太偏执、 2022-03-25 14:28 184阅读 0赞

panic发生时，程序控制权的转移：

package main
    
    import "fmt"
    
    func main() {
    	fmt.Println("Enter function main.")
    	caller1()
    	fmt.Println("Exit function main.")
    }
    
    func caller1() {
    	fmt.Println("Enter function caller1.")
    	caller2()
    	fmt.Println("Exit function caller1.")
    }
    
    func caller2() {
    	fmt.Println("Enter function caller2.")
    	s1 := []int{0, 1, 2, 3, 4}
    	e5 := s1[5]
    	_ = e5
    	fmt.Println("Exit function caller2.")
    }

输出：

panic: runtime error: index out of range
    Enter function main.
    
    Enter function caller1.
    goroutine 1 [running]:
    Enter function caller2.
    main.caller2()
    	E:/GoProgram/awsomeproject/src/go语言核心36讲/19错误处理/2.go:20 +0x98
    main.caller1()
    	E:/GoProgram/awsomeproject/src/go语言核心36讲/19错误处理/2.go:13 +0x6d
    main.main()
    	E:/GoProgram/awsomeproject/src/go语言核心36讲/19错误处理/2.go:7 +0x6d

Go 语言的内建函数recover专用于恢复 panic，或者说平息运行时恐慌。recover函数无需任何参数，并且会返回一个空接口类型的值，这里 的recover需要配合defer使用:

package main
    
    import (
    	"fmt"
    	"errors"
    )
    
    func main() {
    	fmt.Println("Enter function main.")
    	defer func(){
    		fmt.Println("Enter defer function.")
    		if p := recover(); p != nil {
    			fmt.Printf("panic: %s\n", p)
    		}
    		fmt.Println("Exit defer function.")
    	}()
    	// 引发 panic。
    	panic(errors.New("something wrong"))
    	fmt.Println("Exit function main.")
    	
    	/**
    	输出:
    	Enter function main.
    	Enter defer function.
    		panic: something wrong
    	Exit defer function.
    	 */
    }

如果一个函数中有多条defer语句，那么那几个defer函数调用的执行顺序是怎样的？

package main
    
    import "fmt"
    
    func main() {
    	defer fmt.Println("first defer")
    	for i := 0; i < 3; i++ {
    		defer fmt.Printf("defer in for [%d]\n", i)
    	}
    	defer fmt.Println("last defer")
    	/**
    	输出:
    		last defer
    		defer in for [2]
    		defer in for [1]
    		defer in for [0]
    		first defer
    
    	
    	 */
    }