C++文件输入输出流

#include<iostream>
#include<fstream>
#include<cstdlib>
#include<string>
#include<iomanip>
#include"windows.h"
struct student
{
	char name[20];
	int age;
	float height;
};
using namespace std;
int main()
{
	/*********************文本读取方式*********************************/
	string filename;
	cout << "please input a filename you want to read:";
	getline(cin, filename);
	ifstream fin;
	fin.open(filename.c_str(), ios_base::in);
	if (fin.is_open())
	{
		cout << "The content of name.txt is:\n";
		char ch;
		while (fin.get(ch))
			cout << ch;
		cout << endl;
		fin.close();
	}
	ofstream fout(filename.c_str(), ios::out | ios::app);
	if (!fout.is_open())
	{
		cout << "File " << filename << " can't open.\n";
		exit(EXIT_FAILURE);
	}
	cout << "please input another name for student:\n";
	string newname;
	while (getline(cin, newname) && newname.size()>0)
	{
		fout << newname << endl;
	}
	fout.close();
	fin.clear();
	fin.open(filename.c_str());
	if (fin.is_open())
	{
		cout << "The new content of name.txt is:\n";
		char ch;
		while (fin.get(ch))
			cout << ch;
		cout << endl;
		fin.close();
	}
	/*********************二进制读取方式*******************************/
	//这种适合于结构或者类数据读取方式，将整个对象内存量作为一个单位
	string anotherfile;
	cout << "please input a filename and it will be created.\n";
	getline(cin, anotherfile);
	fstream bfout(anotherfile.c_str(), ios::out | ios::app | ios::binary);
	if (!bfout.is_open())
	{
		cout << "This file can't be open.\n";
		exit(EXIT_FAILURE);
	}
	student stu;
	int cnt = 0;
	cout << "please input student's name(a blank line to quit):";
	cin.getline(stu.name, 20);
	while (stu.name[0] != '\0')
	{
		cnt++;
		cout << "please input student's age:";
		cin >> stu.age;
		cout << "please input student's height:";
		(cin >> stu.height).get();
		bfout.write((char *)&stu, sizeof(stu));
		cout << "please input student's name:(a blank line to quit)";
		cin.getline(stu.name, 20);
	}
	bfout.close();
	ifstream bfin;
	bfin.clear();
	bfin.open(anotherfile.c_str(), ios::in | ios::binary);
	if (bfin.is_open())
	{
		cout << "The content of file Student.txt is:\n";
		while (bfin.read((char *)&stu, sizeof stu))
		{
			cout.setf(ios_base::left, ios_base::adjustfield);
			cout << "  Name:" << setw(10) << stu.name << endl;
			cout << "   Age:" << setw(3) << stu.age << endl;
			cout << "Height:" << setw(5)<<setprecision(4) << stu.height << endl;
		}
		bfin.close();
	}
  /*********************随机读取方式**********************************/
	fstream bf(anotherfile.c_str(), ios::in | ios::out | ios::binary);
	if (bf.is_open())
	{
		bf.seekg(0);//以字节为单位
		cout << "The following is content of file " << anotherfile << ":\n";
		while (bf.read((char *)&stu, sizeof stu))
		{
			cout.setf(ios_base::left, ios_base::adjustfield);
			cout << "  Name:" << setw(10) << stu.name << endl;
			cout << "   Age:" << setw(3) << stu.age << endl;
			cout << "Height:" << setw(5) << setprecision(4) << stu.height << endl;
		}
		if (bf.eof())
			bf.clear();
		else
		{
			cerr << "Error in read file" << anotherfile << endl;
			exit(EXIT_FAILURE);
		}
	}
	else
	{
		cerr << anotherfile << " can't be opened.\n";
		exit(EXIT_FAILURE);
	}
	int position;//选择读取位置
	cout << "please input this position you want to modify:";
	(cin >> position).get();
	if (position < 0 || position >= cnt)
	{
		cerr << "Invaild record number.\n";
		exit(EXIT_FAILURE);
	}
	streampos pos = position*sizeof(struct student);
	bf.seekg(pos);
	bf.read((char *)&stu, sizeof stu);
	cout << "Your selection is:\n";
	cout.setf(ios_base::left, ios_base::adjustfield);
	cout << "  Name:" << setw(10) << stu.name << endl;
	cout << "   Age:" << setw(3) << stu.age << endl;
	cout << "Height:" << setw(5) << setprecision(4) << stu.height << endl;
	cout << "Next to modify content.\n";
	cout << "please input student's name:(a blank line to quit)";
	cin.getline(stu.name, 20);
	cout << "please input student's age:";
	cin >> stu.age;
	cout << "please input student's height:";
	(cin >> stu.height).get();
	bf.seekg(pos);//seekp()相对于文件结束的字节位置
	bf.write((char *)&stu, sizeof(stu));
	if (bf.fail())
	{
		cerr << "Error to attempt write.\n";
		exit(EXIT_FAILURE);
	}
	streampos nowpos = bf.tellg();//tellp()返回离文件结束位置字节数
	cout << "Now, the file's pointer is located in " << nowpos << " bytes.\n";
	bf.seekg(0);//以字节为单位，0代表第一个
	cout << "The following is now content of file " << anotherfile << ":\n";
	while (bf.read((char *)&stu, sizeof stu))
	{
		cout.setf(ios_base::left, ios_base::adjustfield);
		cout << "  Name:" << setw(10) << stu.name << endl;
		cout << "   Age:" << setw(3) << stu.age << endl;
		cout << "Height:" << setw(5) << setprecision(4) << stu.height << endl;
	}
	if (bf.eof())
		bf.clear();
	else
	{
		cerr << "Error in read file" << anotherfile << endl;
		exit(EXIT_FAILURE);
	}
  system("pause");
  return 0;
}

程序运行结果如下

please input a filename you want to read:name.txt
The content of name.txt is:
Tom
Jack
Jerry
lucy
Chirsmas
please input another name for student:
China
Russia

The new content of name.txt is:
Tom
Jack
Jerry
lucy
ChirsmasChina
Russia

please input a filename and it will be created.
Student.txt
please input student's name(a blank line to quit):NameA
please input student's age:21
please input student's height:173.34
please input student's name:(a blank line to quit)NameB
please input student's age:23
please input student's height:175.2
please input student's name:(a blank line to quit)
The content of file Student.txt is:
  Name:NameA
   Age:21
Height:173.3
  Name:NameB
   Age:23
Height:175.2
The following is content of file Student.txt:
  Name:NameA
   Age:21
Height:173.3
  Name:NameB
   Age:23
Height:175.2
please input this position you want to modify:1
Your selection is:
  Name:NameB
   Age:23
Height:175.2
Next to modify content.
please input student's name:(a blank line to quit)NameC
please input student's age:19
please input student's height:172.5
Now, the file's pointer is located in 56 bytes.
The following is now content of file Student.txt:
  Name:NameA
   Age:21
Height:173.3
  Name:NameC
   Age:19
Height:172.5
请按任意键继续. . .