[C++知识库]c++ txt文件读取与写入

#include <fstream>

using std::istringstream;
using std::ifstream;
using std::ofstream;
using std::ostringstream;

头文件fstream，四个类型。

istringstream：字符串流类型

ifstream：读入文件内的字符串流

ofstream：打开一个文件，默认是截取，即文件的旧数据被丢弃。

? ? ? ? ? ? ? ? 因此可以用ofstream::app，app（append）追加、添加。

ostringstream：输出流，可以用<<不断向其添加字符串。

#include "mylib7.h"
#include <fstream>

using std::istringstream;
using std::ifstream;
using std::ofstream;
using std::ostringstream;

int main() {
	string file1 = "s.txt";//filename
	string file2 = "s2.txt";
	ifstream input(file1);//input is the file1's contents
	ofstream out;//out is a file will be writen
	ostringstream ofile;//ofile is a stream to store strings
	string line;
	string word;
	vector<string> vst;
	string::size_type cnt=0;
	while (getline(input, line)) {//take a line from stream input to line
		vst.push_back(line);
		++cnt;
		
		istringstream record(line);//make the record to store line's content
		while (record >> word) {
		
			cout << word<<' ';
			ofile << word << ' ';//add string to ostream ofile
		}
		cout << endl;
		ofile << endl;
		
	}
	for (int i = 0; i < cnt; ++i) {
	
		istringstream record(vst[i]);
		while (record >> word) {

			cout << word << ' ';
		}
		cout << endl;
	}
	out.open(file2, ofstream::app);//open file2 by append
	out << ofile.str();
	out.close();

		
		


}