Golang學習筆記_20——error
Golang學習筆記_21——Reader
Golang學習筆記_22——Reader示例

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error補充

1. 基本錯誤處理

在Go中，函數通常返回兩個值：一個是預期的結果，另一個是error類型的值。
如果函數執行過程中發生錯誤，error值將不為nil。

func divide(a, b float64) (float64, error) {if b == 0 {return 0, errors.New("division by zero")}return a / b, nil
}func error_demo_1() {// 調用 divide 函數進行除法運算result, err := divide(10, 0)if err != nil {// 處理錯誤println("Error:", err)} else {// 輸出結果println("Result:", result)}
}

測試方法

func Test_error_demo_1(t *testing.T) {error_demo_1()
}

輸出結果

=== RUN   Test_error_demo_1
Error: (0x105134bc8,0x1400009ef48)
--- PASS: Test_error_demo_1 (0.00s)
PASS

2. 自定義錯誤

自定義錯誤類型可以實現error接口，該接口僅包含一個Error方法，返回一個字符串。

// 自定義錯誤
type MyError2 struct {When stringwhat string
}func (e *MyError2) Error() string {return fmt.Sprintf("when: %s, what: %s", e.When, e.what)
}func testMyError() error {err := &MyError2{When: "now",what: "something wrong",}return err
}

測試方法

func Test_testMyError(t *testing.T) {if err := testMyError(); err != nil {fmt.Println(err)}
}

輸出結果

=== RUN   Test_testMyError
when: now, what: something wrong
--- PASS: Test_testMyError (0.00s)
PASS

3. 錯誤類型判斷

3.1 類型斷言

// MyError2 是自定義錯誤類型func ErrorAssertDemo() error {err := &MyError2{When: "now",what: "something wrong",}return err
}func TestErrorAssertDemo() {err := ErrorAssertDemo()if specificErr := err.(*MyError2); specificErr != nil {fmt.Println("specificErr:", specificErr)} else {fmt.Println("normalErr:", err)}
}

測試方法

func Test_ErrorAssertDemo(t *testing.T) {TestErrorAssertDemo()
}

輸出結果

=== RUN   Test_ErrorAssertDemo
specificErr: when: now, what: something wrong
--- PASS: Test_ErrorAssertDemo (0.00s)
PASS

3.2 類型選擇

// 錯誤類型選擇
// MyError2 是自定義錯誤類型
func ErrorTypeDemo1() error {return &MyError2{When: "now",what: "myError wrong",}
}func ErrorTypeDemo2() error {return errors.New("normal wrong")
}func switchErrorDemo(err error) {if err != nil {switch err1 := err.(type) {case *MyError2:fmt.Println("myError2:", err1)default:fmt.Println("normal:", err1)}}
}func TestErrorTypeDemo() {err1 := ErrorTypeDemo1()err2 := ErrorTypeDemo2()switchErrorDemo(err1)switchErrorDemo(err2)
}

測試方法

func Test_ErrorTypeDemo(t *testing.T) {TestErrorTypeDemo()
}

輸出結果

=== RUN   Test_ErrorTypeDemo
myError2: when: now, what: myError wrong
normal: normal wrong
--- PASS: Test_ErrorTypeDemo (0.00s)
PASS

4. panic && recover

在Go中，panic用于表示一個不可恢復的運行時錯誤。當panic發生時，程序將停止正常執行，并開始逐級調用已注冊的延遲函數（deferred functions），隨后程序崩潰。
recover是一個內置函數，用于從panic中恢復。它只能在延遲函數中調用。在正常的執行路徑中調用recover將返回nil。

// panic 和 recover
func myPanic() {panic("error happened")
}func safeRecover() {defer func() {if err := recover(); err != nil {fmt.Println("recover:", err)}}()myPanic()
}

測試方法

func Test_safeRecover(t *testing.T) {safeRecover()fmt.Println("after recover")}

輸出結果

=== RUN   Test_safeRecover
recover: error happened
after recover
--- PASS: Test_safeRecover (0.00s)
PASS

源碼

// error_demo_2.go 文件
package error_demoimport ("errors""fmt"
)func divide(a, b float64) (float64, error) {if b == 0 {return 0, errors.New("division by zero")}return a / b, nil
}func errorDemo1() {// 調用 divide 函數進行除法運算result, err := divide(10, 0)if err != nil {// 處理錯誤println("Error:", err)} else {// 輸出結果println("Result:", result)}
}// 自定義錯誤
type MyError2 struct {When stringwhat string
}func (e *MyError2) Error() string {return fmt.Sprintf("when: %s, what: %s", e.When, e.what)
}func testMyError() error {err := &MyError2{When: "now",what: "something wrong",}return err
}func ErrorAssertDemo() error {err := &MyError2{When: "now",what: "something wrong",}return err
}func TestErrorAssertDemo() {err := ErrorAssertDemo()if specificErr := err.(*MyError2); specificErr != nil {fmt.Println("specificErr:", specificErr)} else {fmt.Println("normalErr:", err)}
}// 類型選擇
func ErrorTypeDemo1() error {return &MyError2{When: "now",what: "myError wrong",}
}func ErrorTypeDemo2() error {return errors.New("normal wrong")
}func switchErrorDemo(err error) {if err != nil {switch err1 := err.(type) {case *MyError2:fmt.Println("myError2:", err1)default:fmt.Println("normal:", err1)}}
}func TestErrorTypeDemo() {err1 := ErrorTypeDemo1()err2 := ErrorTypeDemo2()switchErrorDemo(err1)switchErrorDemo(err2)
}// panic 和 recoverfunc myPanic() {panic("error happened")
}func safeRecover() {defer func() {if err := recover(); err != nil {fmt.Println("recover:", err)}}()myPanic()
}

// error_demo_2_test.go 文件
package error_demoimport ("fmt""testing"
)func Test_error_demo_1(t *testing.T) {errorDemo1()
}func Test_testMyError(t *testing.T) {if err := testMyError(); err != nil {fmt.Println(err)}
}func Test_ErrorAssertDemo(t *testing.T) {TestErrorAssertDemo()
}func Test_ErrorTypeDemo(t *testing.T) {TestErrorTypeDemo()
}func Test_safeRecover(t *testing.T) {safeRecover()fmt.Println("after recover")}