使用ifstream和getline读取文件内容、忽略注释读取文件[c++]

拼搏现实的明天。 2022-05-11 07:40 200阅读 0赞

假设有一个叫 **data.txt** 的文件, 它包含以下内容:   
![None.gif][]

Fry: One Jillion dollars.
    [Everyone gasps.]
    #Auctioneer: Sir, that's not a number.
    数据读取， 测试 。

以下就是基于 data.txt 的数据读取操作:

#include <iostream>
    #include <fstream>
    #include <string>
    
    using namespace std;
    
    //输出空行
    void OutPutAnEmptyLine()
    {
        cout<<"\n";
    }
    
    //读取方式: 逐词读取, 词之间用空格区分
    //read data from the file, Word By Word
    //when used in this manner, we'll get space-delimited bits of text from the file
    //but all of the whitespace that separated words (including newlines) was lost. 
    void ReadDataFromFileWBW()
    {
        ifstream fin("data.txt");  
        string s;  
        while( fin >> s ) 
        {    
            cout << "Read from file: " << s << endl;  
        }
    }
    
    //读取方式: 逐行读取, 将行读入字符数组, 行之间用回车换行区分
    //If we were interested in preserving whitespace, 
    //we could read the file in Line-By-Line using the I/O getline() function.
    void ReadDataFromFileLBLIntoCharArray()
    {
        ifstream fin("data.txt"); 
        const int LINE_LENGTH = 100; 
        char str[LINE_LENGTH];  
        while( fin.getline(str,LINE_LENGTH) )
        {    
            cout << "Read from file: " << str << endl;
        }
    }
    
    //读取方式: 逐行读取, 将行读入字符串, 行之间用回车换行区分
    //If you want to avoid reading into character arrays, 
    //you can use the C++ string getline() function to read lines into strings
    void ReadDataFromFileLBLIntoString()
    {
        ifstream fin("data.txt");  
        string s;  
        while( getline(fin,s) )
        {    
            cout << "Read from file: " << s << endl; 
        }
    }
    
    //读取方式: 逐行读取, 将行读入字符串, 行之间用回车换行区分，忽略注释
      If you want to avoid reading into character arrays,
      you can use the C++ string getline() function to read lines into strings
      void ReadDataFromFileLBLIntoStringIgnoreComment()
      {
          ifstream fin("data.txt");
          string s;
          while( getline(fin,s) )
          {
              if(s[0]=='#')
                  continue;
              else
              cout << "Read from file: " << s << endl;
          }
      }
    
    
    //带错误检测的读取方式
    //Simply evaluating an I/O object in a boolean context will return false 
    //if any errors have occurred
    void ReadDataWithErrChecking()
    {
        string filename = "dataFUNNY.txt";  
        ifstream fin( filename.c_str());  
        if( !fin ) 
        {   
            cout << "Error opening " << filename << " for input" << endl;   
            exit(-1);  
        }
    }
    
    int main()
    {
        ReadDataFromFileWBW(); //逐词读入字符串 
        OutPutAnEmptyLine(); //输出空行
    
        ReadDataFromFileLBLIntoCharArray(); //逐词读入字符数组
        OutPutAnEmptyLine(); //输出空行
    
        ReadDataFromFileLBLIntoString(); //逐词读入字符串
        OutPutAnEmptyLine(); //输出空行
    
        ReadDataFromFileLBLIntoStringIgnoreComment();//去注释
    
        OutPutAnEmptyLine(); //输出空行
    
        ReadDataWithErrChecking(); //带检测的读取
        return 0;
    }

**输出结果为:**

Read from file: Fry:
    Read from file: One
    Read from file: Jillion
    Read from file: dollars.
    Read from file: [Everyone
    Read from file: gasps.]
    Read from file: Auctioneer:
    Read from file: Sir,
    Read from file: that's
    Read from file: not
    Read from file: a
    Read from file: number.
    Read from file: 数据读取，
    Read from file: 测试
    Read from file: 。 
    
    Read from file: Fry: One Jillion dollars.
    Read from file: [Everyone gasps.]
    Read from file: Auctioneer: Sir, that's not a number.
    Read from file: 数据读取， 测试 。
    
    Read from file: Fry: One Jillion dollars.
    Read from file: [Everyone gasps.]
    Read from file: Auctioneer: Sir, that's not a number.
    Read from file: 数据读取， 测试 。
    
    Read from file: Fry: One Jillion dollars.
    Read from file: [Everyone gasps.]
    Read from file: 数据读取， 测试 。
    
    Error opening  dataFUNNY.txt for input
    Press any key to continue

[None.gif]: /images/20220511/ab8cb499835d40ddb2a32b80bdf2d2ac.png