#include <iostream>
#include <fstream>
#include <string>
#include <vector>
using namespace std;
class TxtReader
{
    private:        
        ifstream txtfile;
        static const int linesize;
        static const int rowsize;
        vector<fstream::streampos>screenpos;
    public:
        TxtReader(string name);
        void LastScreen();
        void NextScreen();
        void ShowContent();
        ~TxtReader();
};
const int TxtReader::linesize = 22; //一屏22行
const int TxtReader::rowsize = 70; //一行70个字符
TxtReader::TxtReader(string name)
{
   txtfile.open(name.c_str());;
    if(!txtfile)
    {
        cout << "Open file failed!" << endl;
        return;
    }
    screenpos.push_back(txtfile.tellg());
    ShowContent();
}
TxtReader::~TxtReader()
{
    txtfile.close();
}
void TxtReader::ShowContent()
{
    char tmp[rowsize+1];
    int line = 0;
    while((!txtfile.eof())&&(line!=linesize))
    {
        txtfile.getline(tmp, rowsize+1);
        line += 1;
        cout << tmp << endl;
    }
}
void TxtReader::NextScreen()
{
    if(txtfile.eof())
        return;
    screenpos.push_back(txtfile.tellg());
    ShowContent();
}
void TxtReader::LastScreen()
{
    if(screenpos.size() == 1)
        return;
    txtfile.seekg(screenpos.back());
    screenpos.pop_back();
    ShowContent();
}
int main()
{
    cout << "Input the file name to open:" << endl;
    string filename;
    cin >> filename;
    TxtReader reader(filename);
    char control;
    while(cin >> control)
    {
        if(control == 'n')
            reader.NextScreen();
        if(control == 'p')
            reader.LastScreen();
        if(control == 'q')
            break;
    }
}
这个运行不了 求帮助