如何读取文本文件？

我尝试读取“ file.txt”并使用 Golang 将内容放入一个变量中。

package main


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


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


fmt.Print(file)
}

成功读取文件，从 奥斯，打开返回的返回类型为 * os. File

148621 次浏览
小开
最佳答案

It depends on what you are trying to do.

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

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.

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)
}

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
}
}


}

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

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


}
}

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.


提交答案