如何阅读文本文件? [英] How to read a text file?

问题描述

我正在尝试读取"file.txt"，然后使用Golang将内容放入变量中.这是我尝试过的...

I'm trying to read "file.txt" and put the contents into a variable using Golang. Here is what I've tried...

package main

import (
    "fmt"
    "os"
    "log"
)

func main() {
    file, err := os.Open("file.txt")
    if err != nil {
        log.Fatal(err)
    }

    fmt.Print(file)
}

文件已成功读取，并且从 os.Open 返回的返回类型为 * os.File

The file gets read successfully and the return from os.Open returns a type of *os.File

推荐答案

这取决于您要执行的操作.

It depends on what you are trying to do.

file, err := os.Open("file.txt")
fmt.print(file)

之所以输出& {0xc082016240}，是因为您正在打印文件描述符( * os.File )的指针值，而不是文件内容.要获取文件内容，可以从文件描述符中 READ .

The reason it outputs &{0xc082016240}, is because you are printing the pointer value of a file-descriptor (*os.File), not file-content. To obtain file-content, you may READ from a file-descriptor.

要读取所有文件内容(以字节为单位)到内存，请 ioutil.ReadAll

To read all file content(in bytes) to memory, ioutil.ReadAll

package main

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

func main() {
    file, err := os.Open("file.txt")
    if err != nil {
        log.Fatal(err)
    }
    defer func() {
        if err = file.Close(); err != nil {
            log.Fatal(err)
        }
    }()


  b, err := ioutil.ReadAll(file)
  fmt.Print(b)
}

但是有时，如果文件很大，则仅读取块(缓冲区大小)可能会更节省内存:因此，您可以使用 io.Reader.Read 的实现 * os.File

But sometimes, if the file size is big, it might be more memory-efficient to just read in chunks: buffer-size, hence you could use the implementation of io.Reader.Read from *os.File

func main() {
    file, err := os.Open("file.txt")
    if err != nil {
        log.Fatal(err)
    }
    defer func() {
        if err = file.Close(); err != nil {
            log.Fatal(err)
        }
    }()


    buf := make([]byte, 32*1024) // define your buffer size here.

    for {
        n, err := file.Read(buf)

        if n > 0 {
            fmt.Print(buf[:n]) // your read buffer.
        }

        if err == io.EOF {
            break
        }
        if err != nil {
            log.Printf("read %d bytes: %v", n, err)
            break
        }
    }

}

否则，您也可以使用标准的util软件包: bufio ，尝试使用 Scanner . Scanner 使用令牌(分隔符)读取文件.

Otherwise, you could also use the standard util package: bufio, try Scanner. A Scanner reads your file in tokens: separator.

默认情况下，扫描程序将令牌按换行符前进(当然，您可以自定义扫描程序应如何对文件进行令牌化，请从此处了解 bufio测试).

By default, scanner advances the token by newline (of course you can customise how scanner should tokenise your file, learn from here the bufio test).

package main

import (
    "fmt"
    "os"
    "log"
    "bufio"
)

func main() {
    file, err := os.Open("file.txt")
    if err != nil {
        log.Fatal(err)
    }
    defer func() {
        if err = file.Close(); err != nil {
            log.Fatal(err)
        }
    }()

    scanner := bufio.NewScanner(file)

    for scanner.Scan() {             // internally, it advances token based on sperator
        fmt.Println(scanner.Text())  // token in unicode-char
        fmt.Println(scanner.Bytes()) // token in bytes

    }
}

最后，我也想向您推荐这个很棒的网站: go-lang文件备忘单.它包含了与在go-lang中处理文件有关的几乎所有内容，希望您会发现它有用.

Lastly, I would also like to reference you to this awesome site: go-lang file cheatsheet. It encompassed pretty much everything related to working with files in go-lang, hope you'll find it useful.

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