hello-world-19.go

package main

import (
	"bufio"
	"fmt"
	"io"
	"io/ioutil"
	"os"
	"path/filepath"
	"strings"
)

func check(e error) {
	if e != nil {
		panic(e)
	}
}

func readFileDemo() {
	dat, err := ioutil.ReadFile("D:\\GoProject\\gobyExample\\fileTest.txt")
	check(err)
	fmt.Println(string(dat))

	f, err := os.Open("D:\\GoProject\\gobyExample\\fileTest.txt")
	check(err)

	b1 := make([]byte, 5)
	n1, err := f.Read(b1)
	check(err)
	fmt.Printf("%d bytes:%s\n", n1, string(b1[:n1]))

	o2, err := f.Seek(6, 0)
	check(err)
	b2 := make([]byte, 2)
	n2, err := f.Read(b2)
	check(err)
	fmt.Printf("%d bytes @ %d: ", n2, o2)
	fmt.Printf("%v\n", string(b2[:n2]))

	o3, err := f.Seek(6, 0)
	check(err)
	b3 := make([]byte, 2)
	n3, err := io.ReadAtLeast(f, b3, 2)
	check(err)
	fmt.Printf("%d bytes @ %d: %s\n", n3, o3, string(b3))

	// 返回文件起始位置
	_, err = f.Seek(0, 0)
	check(err)

	r4 := bufio.NewReader(f)
	b4, err := r4.Peek(5)
	check(err)
	fmt.Printf("5 bytes: %s\n", string(b4))

	f.Close()

}

func writeFileDemo() {
	d1 := []byte("hello\ngo\n")
	err := ioutil.WriteFile("D:\\GoProject\\gobyExample\\writeFile.txt", d1, 0644)
	check(err)

	f, err := os.Create("D:\\GoProject\\gobyExample\\writeTest1.txt")
	check(err)

	defer f.Close()

	d2 := []byte{115, 111, 109, 101, 10}
	n2, err := f.Write(d2)
	fmt.Printf("wrote %d bytes\n", n2)

	n3, err := f.WriteString("writes\n")
	fmt.Printf("wrote %d bytes\n", n3)
	// 将缓冲的数据写入硬盘
	f.Sync()

	w := bufio.NewWriter(f)
	n4, err := w.WriteString("buffered\n")
	fmt.Printf("wrote %d bytes\n", n4)
	//使用 Flush 来确保，已将所有的缓冲操作应用于底层 writer。
	w.Flush()
}

func filepathDemo() {
	p := filepath.Join("dir1", "dir2", "filename")
	fmt.Println("p:", p)

	fmt.Println(filepath.Join("dir1//", "filename"))
	fmt.Println(filepath.Join("dir1/../dir1", "filename"))

	fmt.Println("Dir(p):", filepath.Dir(p))
	fmt.Println("Base(p):", filepath.Base(p))

	fmt.Println(filepath.IsAbs("dir/file"))
	fmt.Println(filepath.IsAbs("/dir/file"))
	filename := "config.json"
	ext := filepath.Ext(filename)
	fmt.Println(ext)

	fmt.Println(strings.TrimSuffix(filename, ext))

	// 寻找相对路径
	rel, err := filepath.Rel("a/b", "a/b/t/file")
	if err != nil {
		panic(err)
	}
	fmt.Println(rel)
	rel, err = filepath.Rel("a/b", "a/c/t/file")
	if err != nil {
		panic(err)
	}
	fmt.Println(rel)

	rel, err = filepath.Rel("c/b", "a/c/t/file")
	if err != nil {
		panic(err)
	}
	fmt.Println(rel)

}