使用ifstream和getline讀取檔案內容[c++]

maqianmaqian發表於2011-03-16

假設有一個叫 data.txt 的檔案, 它包含以下內容:

Fry: One Jillion dollars.
[Everyone gasps.]
Auctioneer: Sir, that's not a number.
資料讀取, 測試


以下就是基於 data.txt 的資料讀取操作:

#include <iostream>
#include <fstream>
#include <string>

using namespace std;

//輸出空行
void OutPutAnEmptyLine()
{
    cout<<"\n";
}

//讀取方式: 逐詞讀取, 詞之間用空格區分
//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; 
    }
}

//讀取方式: 逐行讀取, 將行讀入字元陣列, 行之間用回車換行區分
//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;
    }
}

//讀取方式: 逐行讀取, 將行讀入字串, 行之間用回車換行區分
//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;
    }
}

//帶錯誤檢測的讀取方式
//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(); //逐詞讀入字串
    OutPutAnEmptyLine(); //輸出空行

    ReadDataFromFileLBLIntoCharArray(); //逐詞讀入字元陣列
    OutPutAnEmptyLine(); //輸出空行

    ReadDataFromFileLBLIntoString(); //逐詞讀入字串
    OutPutAnEmptyLine(); //輸出空行

    ReadDataWithErrChecking(); //帶檢測的讀取
    return 0;
}


輸出結果為:
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:
資料讀取,
Read from file:
測試
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:
資料讀取, 測試

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:
資料讀取, 測試

Error opening  dataFUNNY.txt for input
Press any key to continue

 

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