ifstream操作文件读取_ifstream读取字符串

假设有一个叫  data.txt 的文件, 它包含以下内容: 

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; 
    }
}

// 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

    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 。

Error opening  dataFUNNY.txt for input
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