C++使用ifstream读取txt文件

转自：c++使用getline和ifstream读取文件

#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, W ord B y W ord
// 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 L ine-B y-L ine 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;
}

运行结果