带你粗略了解C++流的读写文件

#include <fstream>
#include <iostream>
#include <string>
using namespace std;
int main()
{
	string name;
	int age;
	ofstream outfile;  //也可以使用fstream, 但是fstream的默认打开方式不截断文件长度
	// ofstream的默认打开方式是,  截断式写入 ios::out |  ios::trunc
	// fstream的默认打开方式是,  截断式写入   ios::out
	// 建议指定打开方式
	outfile.open("user.txt", ios::out | ios::trunc);
	while (1) {
		cout << "[ctrl+z退出]" << endl;
		cout << "请输入姓名:";
		cin >> name;
		if (cin.eof()) { //判断文件是否结束
			break;
		}
		outfile << name << "\t";
		cout << "请输入年龄: ";
		cin >> age;
		outfile << age << endl;  //文本文件写入
	}
	// 关闭打开的文件
	outfile.close();
	system("pause");
	return 0;
}

#include <fstream>
#include <iostream>
#include <string>
using namespace std;
int main()
{
	string name;
	int age;
	ifstream infile;
	infile.open("user.txt");
	while (1) {
		infile >> name;
		if (infile.eof()) { //判断文件是否结束
			break;
		}
		cout << name << "\t";
		infile >> age;
		cout << age << endl;  
	}
	// 关闭打开的文件
	infile.close();
	system("pause");
	return 0;
}

#include <fstream>
#include <iostream>
#include <string>
using namespace std;
int main()
{
	string name;
	int age;
	ofstream outfile;
	outfile.open("user.dat", ios::out | ios::trunc | ios::binary);
	while (1) {
		cout << "请输入姓名: [ctrl+z退出] ";
		cin >> name;
		if (cin.eof()) { //判断文件是否结束
			break;
		}
		outfile << name << "\t";
		cout << "请输入年龄: ";
		cin >> age;  
		//outfile << age << endl;  //会自动转成文本方式写入
		outfile.write((char*)&age, sizeof(age));
	}
	// 关闭打开的文件
	outfile.close();
	system("pause");
	return 0;
}

#include <fstream>
#include <iostream>
#include <string>
using namespace std;
int main()
{
	string name;
	int age;
	ifstream infile;
	infile.open("user.dat", ios::in | ios::binary);
	while (1) {
		infile >> name;
		if (infile.eof()) { //判断文件是否结束
			break;
		}
		cout << name << "\t";
		// 跳过中间的制表符
		char tmp;
		infile.read(&tmp, sizeof(tmp)); 
		//infile >> age; //从文本文件中读取整数, 使用这个方式
		infile.read((char*)&age, sizeof(age));
		cout << age << endl;  //文本文件写入
	}
	// 关闭打开的文件
	infile.close();
	system("pause");
	return 0;
}

#include <fstream>
#include <iostream>
#include <string>
#include <sstream>
using namespace std;
int main()
{
	string name;
	int age;
	ofstream outfile;
	outfile.open("user.txt", ios::out | ios::trunc);
	while (1) {
		cout << "[ctrl+z退出]" << endl;
		cout << "请输入姓名: ";
		cin >> name;
		if (cin.eof()) { //判断文件是否结束
			break;
		}
		cout << "请输入年龄: ";
		cin >> age;
		stringstream s;
		s << "name:" << name << "\t\tage:" << age << endl;
		outfile << s.str();
	}
	// 关闭打开的文件
	outfile.close();
	system("pause");
	return 0;
}

#include <fstream>
#include <iostream>
#include <string>
#include <sstream>
#include <Windows.h>
using namespace std;
int main(void)
{
	char name[32];
	int age;
	string line;
	ifstream infile;
	infile.open("user.txt");
	while (1) {
		getline(infile, line);
		if (infile.eof()) { //判断文件是否结束
			break;
		}
		sscanf_s(line.c_str(), "姓名:%s 年龄:%d", name, sizeof(name),&age);
		cout << "姓名:" << name << "\t\t年龄:" << age << endl;
	}
	infile.close();
	system("pause");
	return 0;
}

#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main(void) {
	ifstream infile;
	infile.open(/*文件名字这里我就不写了*/".cpp");
	if (!infile.is_open()) {
		return 1;
	}
		//定位到最后50个字母
	infile.seekg(-50, infile.end);
	while (!infile.eof()) {
		string line;
		getline(infile, line);
		cout << line << endl;
	}
	infile.close();
	system("pause");
	return 0;
}

#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main(void) {
	ifstream infile;
	infile.open(/*文件名字这里我就不写了*/".cpp");
	if (!infile.is_open()) {
		return 1;
	}
	// 先把文件指针移动到文件尾
	infile.seekg(0, infile.end);
	int len = infile.tellg();
	cout << "len:" << len;
	infile.close();
	system("pause");
	return 0;
}

#include <iostream>
#include <fstream>
#include <string>
using namespace std;
int main(void) {
	ofstream outfile;
	outfile.open("test.txt");
	if (!outfile.is_open()) {
		return 1;
	}
	outfile << "123456789";
	outfile.seekp(4, outfile.beg);
	outfile << "ABC";
	outfile.close();
	system("pause");
	return 0;
}