Go学习:defer

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Go学习:defer

defer的概念

defer调用再函数结束时发生,具体概念可以直接百度或者google详细搜索详细,这里主要是通过几个实例来对defer进行详解.

defer实例

实例1

package mainimport "fmt"func tryDefer() {defer fmt.Println(1)fmt.Println(2)
}func main() {// 2// 1tryDefer()
}

实例2

package mainimport "fmt"func tryDefer() {defer fmt.Println(1)defer fmt.Println(2)fmt.Println(3)
}func main() {// 3// 2// 1tryDefer()
}

实例3

package mainimport "fmt"func tryDefer() {defer fmt.Println(1)defer fmt.Println(2)fmt.Println(3)panic("error test")fmt.Println(4)
}func main() {// 3// 2// 1// panic: error testtryDefer()
}

实例4

package mainimport ("bufio""fmt""learngo/errhandling/fib""os"
)func writeFlie(fileName string) {file, err := os.Create(fileName)if err != nil {panic(err)}defer file.Close()writer := bufio.NewWriter(file)defer writer.Flush()f := fib.Fib()for i := 0; i < 20; i++ {fmt.Fprintln(writer,f())}
}func main() {writeFlie("fib.text")
}

package fibfunc Fib() func() int {a, b := 0, 1return func() int {a, b = b, a+breturn a + b}
}

实例5

package mainimport ("fmt"
)func tryDefer1() {for i := 0; i < 10; i++ {defer fmt.Println(i)if i == 5 {panic("error test")}}
}func main() {// 5// 4// 3// 2// 1// 0// panic: error testtryDefer1()
}

• defer调用确保调用再函数结束时发生
• 参数再defer语句时计算
• defer列表为后进先出

何时使用defer调用

• Open/Close
• Lock/Unlock
• PrintHeader/PrintFooter