读写数据

读取用户的输入

我们如何读取用户的键盘（控制台）输入呢？从键盘和标准输入 os.Stdin 读取输入，最简单的办法是使用 fmt 包提供的 Scan 和 Sscan 开头的函数。

// 从控制台读取输入:
package main
import "fmt"

var (
   firstName, lastName, s string
   i int
   f float32
   input = "56.12 / 5212 / Go"
   format = "%f / %d / %s"
)

func main() {
   fmt.Println("Please enter your full name: ")
   fmt.Scanln(&firstName, &lastName)
   // fmt.Scanf("%s %s", &firstName, &lastName)
   fmt.Printf("Hi %s %s!\n", firstName, lastName) // Hi Chris Naegels
   fmt.Sscanf(input, format, &f, &i, &s)
   fmt.Println("From the string we read: ", f, i, s)
    // 输出结果: From the string we read: 56.12 5212 Go
}

也可以使用 bufio 包提供的缓冲读取（buffered reader）来读取数据，正如以下例子所示：

package main
import (
    "fmt"
    "bufio"
    "os"
)

var inputReader *bufio.Reader
var input string
var err error

func main() {
    inputReader = bufio.NewReader(os.Stdin)
    fmt.Println("Please enter some input: ")
    input, err = inputReader.ReadString(\'\n\')
    if err == nil {
        fmt.Printf("The input was: %s\n", input)
    }
}

读文件写文件

使用os.file来读取文件

package main

import (
    "bufio"
    "fmt"
    "io"
    "os"
)

func main() {
    inputFile, inputError := os.Open("input.dat")
    if inputError != nil {
        fmt.Printf("An error occurred on opening the inputfile\n" +
            "Does the file exist?\n" +
            "Have you got acces to it?\n")
        return // exit the function on error
    }
    defer inputFile.Close()

    inputReader := bufio.NewReader(inputFile)
    for {
        inputString, readerError := inputReader.ReadString(\'\n\')
        fmt.Printf("The input was: %s", inputString)
        if readerError == io.EOF {
            return
        }      
    }
}

读取整个文件到字符串内

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

func main() {
    inputFile := "products.txt"
    outputFile := "products_copy.txt"
    buf, err := ioutil.ReadFile(inputFile)
    if err != nil {
        fmt.Fprintf(os.Stderr, "File Error: %s\n", err)
        // panic(err.Error())
    }
    fmt.Printf("%s\n", string(buf))
    err = ioutil.WriteFile(outputFile, buf, 0644) // oct, not hex
    if err != nil {
        panic(err.Error())
    }
}

带缓冲的读取

buf := make([]byte, 1024)
...
n, err := inputReader.Read(buf)
if (n == 0) { break}

读取压缩文件

package main

import (
	"fmt"
	"bufio"
	"os"
	"compress/gzip"
)

func main() {
	fName := "MyFile.gz"
	var r *bufio.Reader
	fi, err := os.Open(fName)
	if err != nil {
		fmt.Fprintf(os.Stderr, "%v, Can\'t open %s: error: %s\n", os.Args[0], fName,
			err)
		os.Exit(1)
	}
	defer fi.Close()
	fz, err := gzip.NewReader(fi)
	if err != nil {
		r = bufio.NewReader(fi)
	} else {
		r = bufio.NewReader(fz)
	}

	for {
		line, err := r.ReadString(\'\n\')
		if err != nil {
			fmt.Println("Done reading file")
			os.Exit(0)
		}
		fmt.Println(line)
	}
}

写文件

package main

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

func main () {
	// var outputWriter *bufio.Writer
	// var outputFile *os.File
	// var outputError os.Error
	// var outputString string
	outputFile, outputError := os.OpenFile("output.dat", os.O_WRONLY|os.O_CREATE, 0666)
	if outputError != nil {
		fmt.Printf("An error occurred with file opening or creation\n")
		return  
	}
	defer outputFile.Close()

	outputWriter := bufio.NewWriter(outputFile)
	outputString := "hello world!\n"

	for i:=0; i<10; i++ {
		outputWriter.WriteString(outputString)
	}
	outputWriter.Flush()
}