Let's talk about the common error logging mechanisms in Golang

As a constantly evolving language, Golang is constantly introducing new features and adding more libraries, making it the best choice for modern development. However, even the best code can have errors.

For Golang developers, the error log is a very important tool. They allow you to quickly identify errors and fix them, making your application more robust and reliable. However, to use error logs correctly, you need to know how to create, log, and debug them.

This article will introduce the common error logging mechanisms in Golang, including basic error handling, panic/defer mechanism, standard library log and third-party log library, as well as some best practices and debugging skills.

1. Basic error handling
   The basic error handling mechanism in Golang is to use the error type. It is a predefined interface used to represent error information returned by certain functions or methods. If the return value of a function or method contains a value of type error, it means that the operation may have failed. You can use if statements or switch statements to check the error value and take appropriate action. For example:

func openFile(filename string) error {

file, err := os.Open(filename)
if err != nil {
    return err
}
defer file.Close()

return nil

}

In the above code, the function openFile opens a file and returns an error type value. If the file cannot be opened, it will return a non-zero error value. In the main program you can check the returned error value and take appropriate action:

err := openFile("input.txt")
if err != nil {

log.Fatal(err)

}

In this case, the main function calls the openFile function and checks the returned error. If an error occurs, it prints an error message and exits the program.

2. Panic/Defer mechanism
   There is a special mechanism in Golang that can be used when a fatal error occurs in the program: the panic/defer mechanism. When a program runs into an error that cannot be handled, it can call the panic function to raise a panic exception, which will interrupt the execution of the current function and be raised up the call stack until it is properly caught or the program exits. Normally, you should not call the panic function directly. Instead, you should use the defer mechanism to catch the exception and perform some cleanup operations, such as closing the file, releasing memory, etc. For example:

func openFile(filename string) {

file, err := os.Open(filename)
if err != nil {
    panic(err)
}
defer file.Close()

// ... code that uses the file ...

}

In the above code snippet, the function openFile attempts to open a file. If the open fails, it will raise a panic exception. It then uses a defer statement to ensure the file is closed. In the corresponding main function, you can write a recover statement to catch the exception and perform cleanup operations:

func main() {

defer func() {
    if r := recover(); r != nil {
        log.Println("Recovered from panic:", r)
    }
}()

openFile("input.txt")

}

In this case Below, the main function uses a defer statement to ensure that errors are caught in any case. If the openFile function raises an exception, the recover statement will be executed and an error message will be printed.

3. Standard library log
   The Golang standard library contains a very basic logging system: the log package. It has three output functions: Print, Printf and Println. They work the same way, they just format the string differently. For example:

log.Print("Hello, world!")
log.Printf("Hello, %s!", "world")
log.Println("Hello ", "world")

These functions output text to standard output. If you need to write the log file to a file instead of the console, use log.SetOutput:

f, err := os.Create("logfile")
if err != nil {

log.Fatal(err)

}
defer f.Close()
log.SetOutput(f)

This will create a file called logfile and write all log output to that file.

Golang log package also provides some other functions, such as building custom loggers and setting log levels, etc. See the official documentation for details.

4. Third-party log library
   There are many excellent third-party log libraries in the Golang community, such as logrus, zap, zerolog, etc. These libraries provide more features and options such as structured logging, multiple outputs, customizable log levels and field controls, and more. The following is an example code using the logrus library:

import log "github.com/sirupsen/logrus"

func main() {

log.SetFormatter(&log.JSONFormatter{})
log.SetLevel(log.WarnLevel)

log.WithFields(log.Fields{
    "animal": "walrus",
    "size":   10,
}).Info("A group of walrus emerges from the ocean")

}

In this example, we use the logrus library and JSON formatting. Then we set the error level to warning, and then we used the log entry of logrus, we provided some fields, and we recorded the message that a group of walruses emerged from the ocean.

5. Debugging Tips
   When writing code, finding and resolving errors always takes time. Here are some helpful debugging tips that can help you solve problems faster.
6. Use fmt.Printf to print intermediate values.

When you find that the output of your code is not what you expect, you can use fmt.Printf to try to identify the problem. For example:

func foo() {

for i := 0; i < 10; i++ {
    fmt.Printf("%d\n", i)
}

}

In this case, the foo function will output the selected number in each iteration of the loop, thus Help us identify the problem.

2. 使用log.Println或log.Printf记录哪一步失败了。

在某些情况下，您的代码可能会因多个原因之一而失败。使用log.Println或log.Printf来记录当前执行的代码行可以帮助您定位错误。例如：

func openFile(filename string) error {

log.Printf("Trying to open file %s", filename)
file, err := os.Open(filename)
if err != nil {
    log.Printf("Failed to open file %s: %s", filename, err)
    return err
}
defer file.Close()

return nil

}

在这种情况下，函数openFile在尝试打开文件之前记录了它正在尝试打开的文件名。如果出现错误，它还将记录哪个文件无法正常打开。

3. 使用GDB进行调试。

如果您需要深入调试代码，GDB可能是您需要的工具。它是一个强大的调试器，可以与Golang程序一起使用。例如：

$ go build -gcflags "-N -l" -o myprogram
$ gdb ./myprogram

使用上面的命令编译您的Golang程序和调试器。您还需要添加-gcflags“-N -l”标志以确保GDB可以正确识别调试信息。然后，您可以在GDB命令行中运行程序并在其中设置断点和查看变量等。

总结
对于Golang开发者来说，错误日志是一个非常重要的工具，可以帮助识别和解决问题。本文介绍了Golang中常见的错误日志机制，包括基本的错误处理、panic/defer机制、标准库log和第三方日志库，以及一些最佳实践和调试技巧。无论您是新手还是高级开发人员，正确地使用错误日志机制都是必不可少的。

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