Should golang files be closed?

In the Go programming language, when working with files, a common question is about whether the file should be closed. File closing is a very important issue. If you do not close the file, it may cause some unnecessary trouble. So, in Go language, do we need to close the file explicitly? This article will explore this.

In the Go language, closing a file is very important, because if the file is not closed, some important resources may be exhausted. When a file is opened, the operating system kernel will allocate some resources to process the file, including file descriptors and memory buffers. If the files are not closed, these resources may be occupied for a long time, leading to problems such as insufficient system resources and application crashes.

In order to prevent this from happening, the Go language needs to explicitly close the file in the program. If you open a file and do not want to continue working on it, you should close the file immediately. In the Go language, files can be closed through the defer statement, which ensures that the file closing statement will be called before the function ends.

The following is a simple example:

package main

import (
    "fmt"
    "os"
)

func main() {
    file, err := os.Open("example.txt")
    if err != nil {
        fmt.Println("Error:", err)
        return
    }
    defer file.Close()
    // 对文件进行操作
}

In this example, the defer statement is used to close the file, so that no matter what happens in the middle of the function, the file will eventually be ensured to be closed. If you use os.OpenFile() to open the file, you can also close the file in a similar way to the example above.

So under what circumstances should the file be closed? In fact, you should close an open file as soon as you no longer need access to it. This includes the following situations:

1. File reading completed

If you read the end of the file when reading the file, then the file can be considered to have been read. After reading is completed, the file should be closed at this time.

package main

import (
    "fmt"
    "os"
)

func main() {
    file, err := os.Open("example.txt")
    if err != nil {
        fmt.Println("Error:", err)
        return
    }
    defer file.Close()

    // 读取文件
    data := make([]byte, 100)
    count, err := file.Read(data)
    if err == io.EOF {
        fmt.Println("File read finished")
    }

    // 对读取的内容进行处理
    ... 
}

2. File writing completed

If you have written all the content that needs to be written into the file when writing the file, then this file can be considered The writing has been completed and the file should be closed at this time.

package main

import (
    "fmt"
    "os"
)

func main() {
    file, err := os.Create("example.txt")
    if err != nil {
        fmt.Println("Error:", err)
        return
    }
    defer file.Close()

    // 写入数据
    data := []byte("Hello, World!")
    file.Write(data)

    // 写入数据完成
    fmt.Println("Finished writing data to file")
}

3. File is closed abnormally

During the process of processing the file, some abnormal situations may occur, such as abnormal program crash, etc. At this time, the file should be closed. This ensures the security of file operations and prevents other operations from failing due to files being occupied.

package main

import (
    "fmt"
    "os"
)

func main() {
    file, err := os.Open("example.txt")
    if err != nil {
        fmt.Println("Error:", err)
        return
    }
    defer func() {
        if file != nil {
            file.Close()
        }
    }()

    // 处理文件
    ...
}

In summary, closing files is very important in Go language. Pay attention to closing files at appropriate times to ensure program security and good resource management. For Go developers who are used to defers, this is not an insurmountable problem. Because defer closing files has generally become a conscious standard among programmers.

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