如何将日志写入文件 [英] How to write log to file

问题描述

我正在尝试使用Go写入日志文件.

I'm trying to write to a log file with Go.

我尝试了几种方法，但都失败了.这是我尝试过的:

I have tried several approaches, all of which have failed. This is what I have tried:

func TestLogging(t *testing.T) {
    if !FileExists("logfile") {
        CreateFile("logfile")
    }
    f, err := os.Open("logfile")
    if err != nil {
        t.Fatalf("error: %v", err)
    }

    // attempt #1
    log.SetOutput(io.MultiWriter(os.Stderr, f))
    log.Println("hello, logfile")

    // attempt #2
    log.SetOutput(io.Writer(f))
    log.Println("hello, logfile")

    // attempt #3
    log.SetOutput(f)
    log.Println("hello, logfile")
}

func FileExists(name string) bool {
    if _, err := os.Stat(name); err != nil {
       if os.IsNotExist(err) {
            return false
        }
    }
    return true
}

func CreateFile(name string) error {
    fo, err := os.Create(name)
    if err != nil {
        return err
    }
    defer func() {
        fo.Close()
    }()
    return nil
}

已创建日志文件，但没有任何打印或附加的内容.为什么?

The log file gets created, but nothing ever gets printed or appended to it. Why?

推荐答案

os.Open()过去的工作方式一定不同，但这对我有用:

os.Open() must have worked differently in the past, but this works for me:

f, err := os.OpenFile("testlogfile", os.O_RDWR | os.O_CREATE | os.O_APPEND, 0666)
if err != nil {
    log.Fatalf("error opening file: %v", err)
}
defer f.Close()

log.SetOutput(f)
log.Println("This is a test log entry")

基于Go文档，os.Open()不适用于log.SetOutput，因为它会打开文件供读取:"

Based on the Go docs, os.Open() can't work for log.SetOutput, because it opens the file "for reading:"

func Open

func Open(name string) (file *File, err error) Open打开命名的 文件以供阅读.如果成功，返回文件上的方法可以是 用于阅读；关联的文件描述符的模式为O_RDONLY.如果 出现错误，它将是*PathError类型.

func Open(name string) (file *File, err error) Open opens the named file for reading. If successful, methods on the returned file can be used for reading; the associated file descriptor has mode O_RDONLY. If there is an error, it will be of type *PathError.

编辑

将defer f.Close()移动到if err != nil检查之后

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