golang一些常用库(2)

goCopy codepackage main

import (
	"fmt"
	"sync"
	"time"
)

func main() {
	var wg sync.WaitGroup
	var mu sync.Mutex

	for i := 0; i < 5; i++ {
		wg.Add(1)
		go func(i int) {
			defer wg.Done()
			mu.Lock()
			defer mu.Unlock()
			fmt.Println("Goroutine", i, "is working.")
		}(i)
	}

	wg.Wait()
}

goCopy codepackage main

import (
	"fmt"
	"io/ioutil"
)

func main() {
	content := []byte("Hello, Golang!")

	err := ioutil.WriteFile("example.txt", content, 0644)
	if err != nil {
		panic(err)
	}

	readContent, err := ioutil.ReadFile("example.txt")
	if err != nil {
		panic(err)
	}

	fmt.Println("File content:", string(readContent))
}

goCopy codepackage main

import (
	"fmt"
	"strconv"
)

func main() {
	str := "42"
	num, err := strconv.Atoi(str)
	if err == nil {
		fmt.Println("Converted number:", num)
	}

	// 整数转字符串
	newStr := strconv.Itoa(123)
	fmt.Println("Converted string:", newStr)
}

goCopy codepackage main

import (
	"log"
)

func main() {
	log.Print("This is a log message.")
	log.Printf("Logging with format: %s", "Golang")
	log.Fatal("Fatal error. The program will exit.")
}

goCopy codepackage main

import (
	"flag"
	"fmt"
)

func main() {
	var name string
	flag.StringVar(&name, "name", "Gopher", "Your name")
	flag.Parse()

	fmt.Println("Hello,", name)
}

goCopy codepackage main

import (
	"context"
	"fmt"
	"time"
)

func main() {
	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
	defer cancel()

	select {
	case <-time.After(3 * time.Second):
		fmt.Println("Operation completed.")
	case <-ctx.Done():
		fmt.Println("Operation canceled:", ctx.Err())
	}
}