go 基本IO接口

package main

import (
	"fmt"
	"io"
	"strings"
)

func ReadFrom(reader io.Reader, num int) ([]byte, error) {
	p := make([]byte, num)
	n, err := reader.Read(p)
	if n > 0 {
		return p[:n], nil
	}
	return p, err
}

func sampleReaderFromString() {
	data, _ := ReadFrom(strings.NewReader("from string"), 12)
	fmt.Println(data)
}

func main() {
	sampleReaderFromString()
}

　　输出：

[102 114 111 109 32 115 116 114 105 110 103]

package main

import (
	"fmt"
	"io"
	"os"
	"strings"
)

func sampleReadFile() {
	file, _ := os.Open("main.go")
	defer file.Close()

	data, _ := ReadFrom(file, 20)
	fmt.Println(string(data))
}
func ReadFrom(reader io.Reader, num int) ([]byte, error) {
	p := make([]byte, num)
	n, err := reader.Read(p)
	if n > 0 {
		return p[:n], nil
	}
	return p, err
}
func sampleReadStdin() {
	fmt.Println("please input from stdin:")
	data, _ := ReadFrom(os.Stdin, 11)
	fmt.Println(data)
}
func sampleReaderFromString() {
	data, _ := ReadFrom(strings.NewReader("from string"), 12)
	fmt.Println(data)
}

func main() {
	//sampleReaderFromString()
	//ampleReadStdin()
	sampleReadFile()
}

　　

 输出：

package main

import