Question

怎么使用ifstream读取文件

Answer 1

#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;
}