【C++】【学习笔记】【004】从另一个小程序说起

ゞ浴缸里的玫瑰 2022-08-13 17:46 109阅读 0赞

#include <iostream>
    #include <fstream>
    
    using namespace std;
    
    // 将一个文件复制到另一个文件
    int file_copy_main()
    {
        ifstream in;
    
        in.open("test.txt");
        if (!in)
        {
            cerr << "打开文件失败！" << endl;
            return 0;
        }
    
        char x;
        while (in >> x)
        {
            cout << x;
        }
    
        cout << endl;
        in.close();
    
        return 0;
    }
    
    // 将键盘输入的信息存入文件
    int str_to_file_main()
    {
        ofstream out;
    
        out.open("test2.txt");
        if (!out)
        {
            cout << "打开文件失败！" << endl;
            return 0;
        }
    
        for (int i = 0; i < 10; i++)
        {
            out << i;
        }
    
        out << endl;
        out.close();
    
        return 0;
    }
    
    int main()
    {
        //file_copy_main();
        str_to_file_main();
        return 0;
    }

ifstream in;in.open("test.txt");与ifstream in("test.txt");的效果相同。

构造函数：就是对象默认使用的函数（方法）。

事实上，它还可以接受不止一个参数！

ifstream in(char \*filename, int open\_mode);

<table style="border-collapse:collapse; margin-top:10px; margin-bottom:10px; background-color:inherit; width:600px"> 
 <tbody style="background-color:inherit"> 
  <tr style="background-color:inherit"> 
   <td style="word-break:break-all; border:1px solid rgb(153,153,153); padding:5px 10px; min-height:25px; min-width:25px; height:25px; background-color:inherit; width:279px"> 
    <div style="min-width:2px; background-color:inherit"> 
     <span style="font-family:SimSun; font-size:18px">打开模式</span> 
    </div> </td> 
   <td style="word-break:break-all; border:1px solid rgb(153,153,153); padding:5px 10px; min-height:25px; min-width:25px; height:25px; background-color:inherit; width:279px"> 
    <div style="min-width:2px; background-color:inherit"> 
     <span style="font-family:SimSun; font-size:18px">作用</span> 
    </div> </td> 
  </tr> 
  <tr style="background-color:inherit"> 
   <td style="word-break:break-all; border:1px solid rgb(153,153,153); padding:5px 10px; min-height:25px; min-width:25px; height:25px; background-color:inherit; width:279px"> 
    <div style="min-width:2px; background-color:inherit"> 
     <span style="font-family:SimSun; font-size:18px">ios::in</span> 
    </div> </td> 
   <td style="word-break:break-all; border:1px solid rgb(153,153,153); padding:5px 10px; min-height:25px; min-width:25px; height:25px; background-color:inherit; width:279px"> 
    <div style="min-width:2px; background-color:inherit"> 
     <span style="font-family:SimSun; font-size:18px">打开一个可读取文件</span> 
    </div> </td> 
  </tr> 
  <tr style="background-color:inherit"> 
   <td style="word-break:break-all; border:1px solid rgb(153,153,153); padding:5px 10px; min-height:25px; min-width:25px; height:25px; background-color:inherit; width:279px"> 
    <div style="min-width:2px; background-color:inherit"> 
     <span style="font-family:SimSun; font-size:18px">ios::out</span> 
    </div> </td> 
   <td style="word-break:break-all; border:1px solid rgb(153,153,153); padding:5px 10px; min-height:25px; min-width:25px; height:25px; background-color:inherit; width:279px"> 
    <div style="min-width:2px; background-color:inherit"> 
     <span style="font-family:SimSun; font-size:18px">打开一个可写入文件</span> 
    </div> </td> 
  </tr> 
  <tr style="background-color:inherit"> 
   <td style="word-break:break-all; border:1px solid rgb(153,153,153); padding:5px 10px; min-height:25px; min-width:25px; height:27px; background-color:inherit; width:279px"> 
    <div style="min-width:2px; background-color:inherit"> 
     <span style="font-family:SimSun; font-size:18px">ios::binary</span> 
    </div> </td> 
   <td style="word-break:break-all; border:1px solid rgb(153,153,153); padding:5px 10px; min-height:25px; min-width:25px; height:27px; background-color:inherit; width:279px"> 
    <div style="min-width:2px; background-color:inherit"> 
     <span style="font-family:SimSun; font-size:18px">以二进制的形式打开一个文件</span> 
    </div> </td> 
  </tr> 
  <tr style="background-color:inherit"> 
   <td style="word-break:break-all; border:1px solid rgb(153,153,153); padding:5px 10px; min-height:25px; min-width:25px; height:25px; background-color:inherit; width:279px"> 
    <div style="min-width:2px; background-color:inherit"> 
     <span style="font-family:SimSun; font-size:18px">ios::app</span> 
    </div> </td> 
   <td style="word-break:break-all; border:1px solid rgb(153,153,153); padding:5px 10px; min-height:25px; min-width:25px; height:25px; background-color:inherit; width:279px"> 
    <div style="min-width:2px; background-color:inherit"> 
     <span style="font-family:SimSun; font-size:18px">写入的所有数据将被追加到文件的末尾</span> 
    </div> </td> 
  </tr> 
  <tr style="background-color:inherit"> 
   <td style="word-break:break-all; border:1px solid rgb(153,153,153); padding:5px 10px; min-height:25px; min-width:25px; height:25px; background-color:inherit; width:279px"> <span style="font-family:SimSun; font-size:18px">ios::trunk</span></td> 
   <td style="word-break:break-all; border:1px solid rgb(153,153,153); padding:5px 10px; min-height:25px; min-width:25px; height:25px; background-color:inherit; width:279px"> 
    <div style="min-width:2px; background-color:inherit"> 
     <span style="font-family:SimSun; font-size:18px">删除文件原来已存在的内容</span> 
    </div> </td> 
  </tr> 
  <tr style="background-color:inherit"> 
   <td style="word-break:break-all; border:1px solid rgb(153,153,153); padding:5px 10px; min-height:25px; min-width:25px; height:25px; background-color:inherit; width:279px"> 
    <div style="min-width:2px; background-color:inherit"> 
     <span style="font-family:SimSun; font-size:18px">ios::nocreate</span> 
    </div> </td> 
   <td style="word-break:break-all; border:1px solid rgb(153,153,153); padding:5px 10px; min-height:25px; min-width:25px; height:25px; background-color:inherit; width:279px"> 
    <div style="min-width:2px; background-color:inherit"> 
     <span style="font-family:SimSun; font-size:18px">如果要打开的文件并不存在，那么以此参数调用open函数将无法进行</span> 
    </div> </td> 
  </tr> 
  <tr style="background-color:inherit"> 
   <td style="word-break:break-all; border:1px solid rgb(153,153,153); padding:5px 10px; min-height:25px; min-width:25px; height:25px; background-color:inherit; width:279px"> 
    <div style="min-width:2px; background-color:inherit"> 
     <span style="font-family:SimSun; font-size:18px">ios::noreplace</span> 
    </div> </td> 
   <td style="word-break:break-all; border:1px solid rgb(153,153,153); padding:5px 10px; min-height:25px; min-width:25px; height:25px; background-color:inherit; width:279px"> 
    <div style="min-width:2px; background-color:inherit"> 
     <span style="font-family:SimSun; font-size:18px">如果要打开的文件已存在，试图用open函数打开时将返回一个错误。</span> 
    </div> </td> 
  </tr> 
 </tbody> 
</table>

// 将字符串存入文件，而后将其存入数组并显示
    int str_to_file_array_main()
    {
        fstream fp("test.txt", ios::in | ios::out);
        if (!fp)
        {
            cout << "打开文件失败！" << endl;
            return 0;
        }
    
        fp << "Ilovecpp.";
    
        static char str[10];
        fp.seekg(ios::beg);
        fp >> str;
        cout << str << endl;
    
        fp.close();
        return 0;
    }
    
    输出：Ilovecpp.