Application of defer keyword of Golang function in exception handling

Golang is a modern programming language whose simple and efficient design style is highly praised by developers. In Golang, the defer keyword of a function is a very useful feature, which can help us clean up some resources before the function returns. Not only that, defer can also play a huge role in exception handling. This article will discuss its application in exception handling.

What is the defer keyword?

In Golang, the defer keyword is used to delay the execution of a function, that is, execute it at the end of the function. To put it simply, it tells the Golang compiler: "Regardless of the success or failure of the execution of this function, this statement must be executed at the end of the function."

The specific implementation method is to use the defer keyword followed by a function call , For example:

func readFile() {
    file, err := os.Open("filename.txt")
    if err != nil {
        log.Fatal(err)
    }
    defer file.Close() // 最后关闭文件 
    // 读取文件内容 
    ...
}

In the above code, we use the defer keyword to close the file. Regardless of whether the file is read successfully or not, this statement will be executed in the end. This avoids problems with forgetting to close files and other resource leaks.

Application of defer in exception handling

In Golang, exception handling uses the panic and recover functions. The so-called panic refers to exceptions actively thrown by the program, and recover is used to capture and handle these exceptions. When dealing with panic, the defer keyword can help us perform some necessary cleanup work, such as closing open files, releasing requested memory, etc.

In the following sample code, we simulate the exception of a file reading function:

func readFile() {
    file, err := os.Open("filename.txt")
    if err != nil {
        log.Fatal(err)
    }
    defer file.Close() // 最后关闭文件 
    // 读取文件内容 
    _, err = file.Read(buf)
    if err != nil {
        panic(err)
    }
}

In the above code, if an exception occurs while reading the file, the panic function will be called to throw An exception occurs and the defer statement will not be executed. However, if we use the recover function for exception handling in the defer statement, we can perform the necessary cleanup work when the program crashes:

func readFile() {
    file, err := os.Open("filename.txt")
    if err != nil {
        log.Fatal(err)
    }
    defer func() {
        if r := recover(); r != nil {
            fmt.Println("程序崩溃了，错误信息为：", r)
            file.Close() // 进行清理工作 
        }
    }()
    // 读取文件内容 
    _, err = file.Read(buf)
    if err != nil {
        panic(err)
    }
}

In the above code, we use an anonymous function to implement defer statement. When the defer statement is executed, if the program crashes or an exception occurs, the anonymous function will be called to handle the exception and perform necessary cleanup work. The recover function is used in this anonymous function to capture exception information and then handle it.

It should be noted that when using defer for exception handling, we need to place it at the beginning of the function as much as possible to ensure that the necessary resource cleanup work has been performed before the program crashes.

Summary

In Golang, the defer keyword of a function can help us perform necessary resource cleanup work, and can also play a huge role in exception handling. Using defer can avoid the problem of forgetting to release resources. At the same time, it also makes exception handling simpler and more efficient. Whether in ordinary function calls or exception handling, defer is a very useful feature, and developers must make full use of it.

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