database.cpp

这是清华出的这本经典的数据结构第三版上的随书例子。希望对大家有用。

#include <iostream>
#include "personal.h"
#include "student.h"
#include "database.h"

template<class T>
Database<T>::Database() {
}

template<class T>
void Database<T>::add(T& d) {
    database.open(fName,ios::in|ios::out|ios::binary);
    database.seekp(0,ios::end);
    d.writeToFile(database);
    database.close();
}

template<class T>
void Database<T>::modify(const T& d) {
    T tmp;
    database.open(fName,ios::in|ios::out|ios::binary);
    while (!database.eof()) {
        tmp.readFromFile(database);
        if (tmp == d) {  // overloaded ==
             cin >> tmp; // overloaded >>
             database.seekp(-d.size(),ios::cur);
             tmp.writeToFile(database);
             database.close();
             return;
        }
    }
    database.close();
    cout << "The record to be modified is not in the database\n";
}

template<class T>
bool Database<T>::find(const T& d) {
    T tmp;
    database.open(fName,ios::in|ios::binary);
    while (!database.eof()) {
        tmp.readFromFile(database);
        if (tmp == d) { // overloaded ==
            database.close();
            return true;
        }
    }
    database.close();
    return false;
}

template<class T>
ostream& Database<T>::print(ostream& out) {
    T tmp;
    database.open(fName,ios::in|ios::binary);
    while (true) { 
        tmp.readFromFile(database);
        if (database.eof())
            break;
        out << tmp << endl; // overloaded <<
    }
    database.close();
    return out;
}

template<class T>
void Database<T>::run() {
    cout << "File name: ";
    cin >> fName;
	cin.ignore();	// skip '\n';
    database.open(fName,ios::in);
	if (database.fail())
		database.open(fName,ios::out);
    database.close();
	char option[5];
    T rec;
    cout << "1. Add 2. Find 3. Modify a record; 4. Exit\n";
    cout << "Enter an option: ";
    while (cin.getline(option,5)) {
		cout<<'['<<option<<']';
        if (*option == '1') {
             cin >> rec;   // overloaded >>
             add(rec);
        }
        else if (*option == '2') {
             rec.readKey();
             cout << "The record is ";
             if (find(rec) == false)
                 cout << "not ";
             cout << "in the database\n";
        }
        else if (*option == '3') {
             rec.readKey();
             modify(rec);
        }
        else if (*option != '4')
             cout << "Wrong option\n";
        else return;
        cout << *this;   // overloaded <<
        cout << "Enter an option: ";
    }
}

int main() {
    Database<Personal>().run();
//  Database<Student>().run();
	return 0;
}