zoukankan      html  css  js  c++  java
  • 5.6 seeking a position within a file 查找文件中的位置

    
    package main
    
    import (
    	"errors"
    	"fmt"
    	"os"
    )
    
    const lineLegth = 25
    
    func main() {
    
    	f, e := os.OpenFile("flatfile.txt", os.O_RDWR|os.O_CREATE, os.ModePerm)
    	if e != nil {
    		panic(e)
    	}
    	defer f.Close()
    
    	fmt.Println(readRecords(2, "last", f))
    	if err := writeRecord(2, "first", "Radomir", f); err != nil {
    		panic(err)
    	}
    	fmt.Println(readRecords(2, "first", f))
    	if err := writeRecord(10, "first", "Andrew", f); err != nil {
    		panic(err)
    	}
    	fmt.Println(readRecords(10, "first", f))
    	fmt.Println(readLine(2, f))
    }
    
    func readLine(line int, f *os.File) (string, error) {
    	lineBuffer := make([]byte, 24)
    	f.Seek(int64(line*lineLegth), 0)
    	_, err := f.Read(lineBuffer)
    	return string(lineBuffer), err
    }
    
    func writeRecord(line int, column, dataStr string, f *os.File) error {
    	definedLen := 10
    	position := int64(line * lineLegth)
    	switch column {
    	case "id":
    		definedLen = 4
    	case "first":
    		position += 4
    	case "last":
    		position += 14
    	default:
    		return errors.New("Column not defined")
    	}
    
    	if len([]byte(dataStr)) > definedLen {
    		return fmt.Errorf("Maximum length for '%s' is %d", column, definedLen)
    	}
    
    	data := make([]byte, definedLen)
    	for i := range data {
    		data[i] = '.'
    	}
    	copy(data, []byte(dataStr))
    	_, err := f.WriteAt(data, position)
    	return err
    }
    
    func readRecords(line int, column string, f *os.File) (string, error) {
    	lineBuffer := make([]byte, 24)
    	f.ReadAt(lineBuffer, int64(line*lineLegth))
    	var retVal string
    	switch column {
    	case "id":
    		return string(lineBuffer[:3]), nil
    	case "first":
    		return string(lineBuffer[4:13]), nil
    	case "last":
    		return string(lineBuffer[14:23]), nil
    	}
    
    	return retVal, errors.New("Column not defined")
    }
    
    /*
     322e 2e4 <nil>
    Radomir.. <nil>
    Andrew... <nil>
    2e2eRadomir... 322e 2e4e <nil>
     */
    
     
     /* file content
     3132 332e 4a75 6e2e 2e2e 2e2e 2e2e 576f
    6e67 2e2e 2e2eRadomir... 322e 2e4e 6f76
    616b 2e2e 2e2e 2e4a 7572 6765 6e2e 2e2e
    2e0a 3130 2e2e 5261 646f 6d69 722e 2e2e
    536f 686c 6963 682e 2e2e 0000 0000 0000
    0000 0000 0000 0000 0000 0000 0000 0000
    0000 0000 0000Andrew.... 0000 0000 0000
    0000 0000 0000 0000 0000 0000 0000 0000
    0000 0000 0000 0000 0000 0000 0000 0000
    0000 0000 0000 0000 0000 0000 0000 0000
    0000 0000 0000 0000 0000 0000 0000 0000
    0000 0000 0000 0000 0000 0000 0000 0000
    0000 0000 0000 0000 0000 0000 0000 0000
    0000 0000 0000 0000 0000 0000 0000 0000
    0000 0000 0000 0000 0000 0000 0000 0000
    0000 0000 0000 0000 0000 0000 0000 416e
    6472 6577 2e2e 2e2e
     
     
     */
    
  • 相关阅读:
    谈谈django里的Contex和RequestContext---向模板里添加全局变量
    Django如何重设Admin密码
    javascript的闭包
    javascript的this用法
    阮一峰---javascript系列
    Javascript继承机制总结 [转]
    chrome浏览器开发者工具使用教程[转]
    WAMP设置默认访问目录
    js 去掉空格.回车.换行
    网站服务器上载目录
  • 原文地址:https://www.cnblogs.com/zrdpy/p/8620959.html
Copyright © 2011-2022 走看看