为什么使用log.Println（“不登录文件”）？

Question

This is my first attempt to log into files with golang.

file, _ := os.Open("logfile")
log.SetOutput(file)
log.Println("foo")

these lines build, but are not working. Why?

Answer 1

Why log.Println(“does not log into file”)?

The reason is because you didn't check the file is exist or not form your code.

file, _ := os.Open("logfile")

you're using _ and didn't check the error. This is important if you wanted to write something in to file. For example look at this code :

    f, err := os.OpenFile(filePath+fileName, os.O_RDWR|os.O_CREATE|os.O_APPEND, os.ModePerm)
    if err != nil {
        // if error then you need to create the file first
        err = os.MkdirAll(filePath, os.ModePerm)
    }

from above code you can see the error checking using if err != nil. if the file is not exist yet then create the file first. using os.MkdirAll().