package main

import (
	"fmt"
)

// defer在函式返回的時候執行,多用於資源釋放(開啟檔案,開啟資料庫連線,函式返回之後,關閉連線)
func testdefer1() {
	defer fmt.Println("hello defer")
	defer fmt.Println("hello defer V2")
	defer fmt.Println("hello defer V3") // 多個defer執行順序是後進先出的棧列
	fmt.Println("aaaaaaaaaaaa")
	fmt.Println("bbbbbbbbbbbb")

}

func testdefer2() {
	for i := 0; i < 5; i++ {
		defer fmt.Printf("i=%d\n", i)
	}
	// 列印順序 4,3,2,1,0
	fmt.Println("running ")
	fmt.Println("return")
}

func testdefer3() {
	var i int = 0
	defer fmt.Printf("testdefer3 defer i=%d\n", i) // 在i=0時,已經寫入defer中了
	i = 1000
	fmt.Printf("testdefer3 i=%d \n", i)
}

func testdefer4() {
	var i int = 0
	defer func(){
		fmt.Printf("testdefer4 defer i=%d\n", i) // 在i=0時,已經寫入defer中了
	}()
	i = 1000
	fmt.Printf("testdefer4 i=%d \n", i)
}

func main() {
	//testdefer1()
	//testdefer2()
	testdefer3()
	testdefer4()
}


 

testdefer3 i=1000
testdefer3 defer i=0
testdefer4 i=1000
testdefer4 defer i=1000