第二十一章流 13seekp()和seekg()函数的结合使用 简单

//第二十一章流 13seekp()和seekg()函数的结合使用
/*#include <iostream>
#include <fstream>
#include <iomanip>
using namespace std;
const int num = 10;
struct people
{
	char name[num];
	int age;
	float pay;
};



const char*file = "people13.txt";
void deleteline(){ while(cin.get() !='\n') continue; }

int main()
{
	//people pp={"陈涛",25,945.34f};	
	//ofstream fout(file,ios::out|ios::binary);
	//fout.write((char*)&pp, sizeof pp);
	//fout.close();
	//people pp1={"李力持",45,1065.58f};
	//fout.open(file,ios::in|ios::out|ios::binary);
	//fout.seekp(sizeof pp, ios::beg);
	//fout.write((char*)&pp1,sizeof pp1);
	//fout.close();

	people pp={0};
	ofstream fout(file,ios::out|ios::binary);
	bool quit = true;
	while(quit)
	{
	    cout<<"输入名称:";
		cin.get(pp.name,num);
		cin.ignore();
		cout<<"输入年龄";
		cin>>pp.age;
		cout<<"输入薪水";
		cin>>pp.pay;
		fout.write((char*)&pp, sizeof pp);
		cout<<"是否继承输入，是按y,否按n:"<<endl;
		char choice;
		cin>>choice;
		if(choice=='y'){
		    deleteline();
			continue;
		}else
			quit = false;	
	}
	fout.close();
	cout<<fixed;




	fstream InOut;
	InOut.open(file,ios::in|ios::out|ios::binary);
	int count=0;
	if(InOut.is_open())
	{
		InOut.seekp(0);//设置函数将指针定位到文件头
		cout<<"当前内容为:"<<file<<endl;
		while(InOut.read((char*)&pp, sizeof pp))
		{
			cout<<count++<<":"<<setw(num)<<pp.name<<":"<<setprecision(0)<<setw(12)<<pp.age<<setprecision(2)<<setw(16)<<pp.pay<<endl;
		}
		if(InOut.eof())//当函数遇到EOF后
		{
			InOut.clear();
		}else{
		    cout<<"读取错误"<<file<<endl;
			exit(EXIT_FAILURE);
		}
	}else{
	    cout<<file<<"不能找开\n";
		exit(EXIT_FAILURE);
	}

	cout<<"输入你希望改变的编号:"<<endl;
	long line;
	cin>>line;
	deleteline();
	if(line<0 || line>=count)
	{
	    cout<<"无效编号"<<endl;
		exit(EXIT_FAILURE);
	}
	streampos place = line*sizeof pp;
	InOut.seekg(place);
	if(InOut.fail()){
	   cout<<"尝试查询失败"<<endl;
	   exit(EXIT_FAILURE);
	}
	InOut.read((char*)&pp, sizeof pp);
	cout<<"你的选择为:";
	cout<<line<<":"<<setw(num)<<pp.name<<":"<<setprecision(0)<<setw(12)<<pp.age<<setprecision(2)<<setw(16)<<pp.pay<<endl;
	if(InOut.eof())
	{
		InOut.clear();
	}

	cout<<"输入名字:"<<endl;
	cin.get(pp.name,num);
	deleteline();

	cout<<"输入年龄:"<<endl;
	cin>>pp.age;
	cout<<"输入薪水"<<endl;
	cin>>pp.pay;

	InOut.seekp(place);
	InOut.write((char*)&pp,sizeof pp)<<flush;
	if(InOut.fail()){
		cout<<"尝试写入失败"<<endl;
		exit(EXIT_FAILURE);
	}

	count=0;
	InOut.seekg(0);
	cout<<"当前内容为:"<<file<<endl;
	while(InOut.read((char*)&pp, sizeof pp))
	{
			cout<<count++<<":"<<setw(num)<<pp.name<<":"<<setprecision(0)<<setw(12)<<pp.age<<setprecision(2)<<setw(16)<<pp.pay<<endl;
	}
	InOut.close();		
	cout<<"完成!";
    return 0;
}*/