Go基础教程系列之defer、panic和recover详解

func main() {
    a()
}

func a() {
    println("in a")
    defer b()              // 将b()压入defer栈中
    println("leaving a")
    //到了这里才会执行b()
}

func b() {
    println("in b")
    println("leaving b")
}

in a
leaving a
in b
leaving b

func a() TYPE{
    ...CODE...
    
    defer b()
    
    ...CODE...
    
    // 函数执行出了错误
    
    return args
    // 函数b()都会在这里执行
}

package main

var x = 10
func main() {
    a()
}

func a() {
	println("start a:",x)   // 输出10
	x = 20
	defer b(x)       // 压栈，并按值拷贝20到栈中
	x = 30
    println("leaving a:",x)  // 输出30
    // 调用defer延迟的对象b()，输出20
}

func b(x int) {
    println("start b:",x)
}

package main

var x = 10

func main() {
	a()
}

func a() int {
	println("start a:", x) // 输出10
	x = 20
	defer func() {      // 压栈，但并未传值，所以内部引用x
		println("in defer:", x)  // 输出30
	}()
	x = 30
	println("leaving a:", x) // 输出30
	return x
}

package main

var x = 10

func main() {
	a()
}

func a() int {
	println("start a:", x) // 输出10
	x = 20
	defer func(x int) {
		println("in defer:", x)  // 输出20
	}(x)
	x = 30
	println("leaving a:", x) // 输出30
	return x
}

func a() int {
	println("start a:", x) // 输出10
	x = 20
	{
		x := 40
		defer func() {
			println("in defer:", x)  // 输出40
		}()
	}
	x = 30
	println("leaving a:", x) // 输出30
	return x
}

func main() {
	println("start...")
	defer println("1")
	defer println("2")
	defer println("3")
	defer println("4")
	println("end...")
}

start...
end...
4
3
2
1

open()
defer file.Close()
... 操作文件 ...

func main() {
	println("start main")
	a()
	println("end main")
}

func a() {
	println("start a")
	panic("panic in a")
	println("end a")
}

start main
start a
panic: panic in a

goroutine 1 [running]:
main.a()
        E:/learning/err.go:14 +0x63
main.main()
        E:/learning/err.go:8 +0x4c
exit status 2

func main() {
    G()
    // 下面的代码会执行
    ...CODE IN MAIN...
}
func G(){
    defer func (){
        if str := recover(); str != nil {
            fmt.Println(str)
        }
    }()
    ...CODE IN G()...
    
    // F()的调用必须在defer关键字之后
    F()
    // 该函数内下面的代码不会执行
    ...CODE IN G()...
}
func F() {
    ...CODE1...
    panic("error found")
    // 下面的代码不会执行
    ...CODE IN F()...
}

func main() {
	println("start main")
	a()
	println("end main")
}

func a() {
	println("start a")
	panic("panic in a")

    // 直接放在panic后是错误的
    panic_str := recover()
    println(panic_str)

	println("end a")
}

package main

import "fmt"

func main() {
	println("start main")
	b()
	println("end main")
}

func a() {
	println("start a")
	panic("panic in a")
	println("end a")
}

func b() {
	println("start b")
	defer func() {
		if str := recover(); str != nil {
			fmt.Println(str)
		}
	}()
	a()
	println("end b")
}

start main
start b
start a
panic in a
end main

$ go doc log Panic
func Panic(v ...interface{})
    Panic is equivalent to Print() followed by a call to panic().