How to use the io/ioutil.WriteFile function in golang to append content to a file

How to use the io/ioutil.WriteFile function in golang to append content to a file

In Go language, use the io/ioutil package The WriteFile function can conveniently write content to a file. However, by default, the WriteFile function will overwrite the original content of the file. If we need to append content to the file instead of overwriting it, we can do it in the following way.

First, we need to open the file and get the contents of the file. Then, add the content we want to append after the original content. Finally, use the WriteFile function to write the new content to the file. The following is a specific code example:

package main

import (
    "fmt"
    "io/ioutil"
    "os"
)

func main() {
    // 定义要写入的内容
    content := []byte("追加的内容")

    // 打开文件，如果文件不存在则创建
    file, err := os.OpenFile("example.txt", os.O_RDWR|os.O_CREATE, 0644)
    if err != nil {
        fmt.Println("打开文件出错：", err)
        return
    }
    defer file.Close()

    // 读取原有内容
    existingContent, err := ioutil.ReadAll(file)
    if err != nil {
        fmt.Println("读取文件出错：", err)
        return
    }

    // 将要追加的内容添加到原有内容之后
    newContent := append(existingContent, content...)

    // 将新内容写入文件
    err = ioutil.WriteFile("example.txt", newContent, 0644)
    if err != nil {
        fmt.Println("写入文件出错：", err)
        return
    }

    fmt.Println("追加内容成功")
}

In the above example, we first use the os.OpenFile function to open the file and set the open mode to os.O_RDWR|os .O_CREATE. This way the file will be created even if it does not exist. Then, we use the ioutil.ReadAll function to read the original content of the file.

Next, we merge the content to be added content and the original content existingContent into newContent. We use the append function to add content to existingContent, and finally get new content.

Finally, we use the ioutil.WriteFile function to write the new content newContent to the file. Please note that here we use example.txt as the file name again, which overwrites the previous content.

If everything goes well, we will see the output as "Append content successful". At this time, the example.txt file will contain the original content and the additional content.

Hope the above code example can help you understand how to append content to a file using the WriteFile function of the io/ioutil package. If you have any questions, please feel free to ask.

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