golang get program error

In program development, error handling is a very important task. When the program encounters an error, it needs to be discovered and handled in time, otherwise the entire program will crash. In Golang, the built-in error handling mechanism can help us better handle program errors. This article explains how to get program errors in Golang.

Error handling

In Golang, errors are regarded as a type, namely the error type. Normally, when a function returns a value of type error, it means that the function may return an error.

The following is a function that returns the length of a string StringLength. When the incoming string is empty, an error will be returned:

func StringLength(str string) (int, error) {
    if str == "" {
        return 0, errors.New("String is empty")
    }
    return len(str), nil
}

In the above code , errors.New method is used to create an object of type error.

When we call StringLength, we need to check whether the returned error object is empty to determine whether the function is executed successfully:

str := "hello world"
length, err := StringLength(str)
if err != nil {
    fmt.Println("Error:", err)
    return
}
fmt.Printf("The length of "%s" is %d
", str, length)

Output:

The length of "hello world" is 11

When the incoming string is empty, the output is:

Error: String is empty

Through the above example, we can see that Golang's error handling mechanism is very intuitive and simple.

Error message details

Sometimes we need to get more detailed information about the error, such as execution error location, error code, etc. In Golang, you can wrap the original error and new error information together through the Wrap function of the errors package, and return a new error value. This new error value carries the original error and custom error information to provide more error details.

Here is an example:

func Divide(x, y float64) (float64, error) {
    if y == 0 {
        return 0, errors.New("division by zero")
    }
    return x / y, nil
}

func main() {
    x, y, err := 4.0, 0.0, error(nil)
    
    // 错误发生在这里
    result, err := Divide(x, y)
    if err != nil {
        err = errors.Wrap(err, "can't perform division")
    }
    fmt.Printf("Result: %v, error: %v", result, err)
}

When an error is wrapped using the Wrap method, it adds a prefix and returns a new error object containing the original error and New error message. In this example, we use the Wrap method and prefix the new error message with "can't perform division".

The error message output at this time is as follows:

Result: 0, error: can't perform division: division by zero

As you can see, the error message contains customized error information and original error information.

panic

When a Goroutine encounters an unrecoverable error or exception, you can use the panic function to pass an error message upward and terminate the execution of the program. Any upper-level function has the opportunity to handle this error or pass it to a higher-level function until the program stops running.

The following is an example:

func processFile(filename string) error {
    file, err := os.Open(filename)
    if err != nil {
        return errors.Wrap(err, "can't open file")
    }
    defer file.Close()

    // ... process file

    if err != nil {
        panic(errors.Wrap(err, "can't process file"))
    }

    return nil
}

In the above code, when file processing fails, we use the panic function to report the error and hope that other Goroutines or programs Can handle it. You can use the recover function in the code that calls processFile to capture panic and perform error handling.

func main() {
    defer func() {
        if p := recover(); p != nil {
            fmt.Printf("Recovered from panic: %v
", p)
        }
    }()

    err := processFile("test.txt")
    if err != nil {
        fmt.Println(err)
    }
}

The above program can run normally, but when an error occurs, panic information will be printed and captured with the recover function.

Summary

In Golang, error handling is a very important task. You can determine whether the function executed successfully by returning a value of type error and checking whether it is empty. When you need to get more error details, you can use the Wrap function for wrapping. When Goroutine encounters an unrecoverable error or exception, you can use the panic function to pass error information upward and terminate the execution of the program.

No matter what the situation is, it is very important to detect and handle errors in time. Only in this way can the reliability and stability of the program be guaranteed.

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