new coder using Dev C++

This is a discussion on new coder using Dev C++ within the C++ Programming forums, part of the General Programming Boards category; Fist Part I am trying to work on a simple database project which needs to determine if a record is ...

  1. #1
    Registered User
    Join Date
    Jul 2006
    Posts
    1

    new coder using Dev C++

    Fist Part
    I am trying to work on a simple database project which needs to determine if a record is null. I am wanting to do this by using the function isNull() in the classes Personal and Student to determine that a record is null. Then overwrite the record to be deleted by a null record. A null record can be defined as having nonnumeric characters (a tombstone) in the first position of the SSN member.

    Second Part
    Then I would like to define the function remove() in the Database which should locate the position of a record to be deleted and overwrite it with a null record. Then after a session is finshed. I would like to invoke a database destructor which copies the nonnull records to a new data file, deletes the old data file, and renames the new data file with the name of the old data file.

    Here is what I have so far... Any help with code, advice, or tips would be greatly appreciated...
    Code:
    ************************ personal.h *********************
    public:
    Personal();
    Personal(char*,char*,char*,int,long);
    void writeToFile(fstream&) const;
    void readFromFile(fstream&);
    void readKey();
    int size() const {
    return 9 + nameLen + cityLen + sizeof(year) + sizeof(salary);
    }
    bool operator==(const Personal& pr) const {
    return strcmp(pr.SSN,SSN) == 0;
    }
    protected:
    const int nameLen, cityLen;
    char SSN[10], *name, *city;
    int year;
    long salary;
    ostream& writeLegibly(ostream&);
    friend ostream& operator<<(ostream& out, Personal& pr) {
    return pr.writeLegibly(out);
    }
    istream& readFromConsole(istream&);
    friend istream& operator>>(istream& in, Personal& pr) {
    return pr.readFromConsole(in);
    }
    };
    
    #endif
    
    ****************** personal.cpp *******************
    
    #include 
    #include "personal.h"
    
    Personal::Personal() : nameLen(10), cityLen(10) {
    name = new char[nameLen+1];
    city = new char[cityLen+1];
    }
    
    Personal::Personal(char ........n, char *n, char *c, int y, long s) :
    nameLen(10), cityLen(10) {
    name = new char[nameLen+1];
    city = new char[cityLen+1];
    strcpy(SSN,ssn);
    strcpy(name,n);
    strcpy(city,c);
    year = y;
    salary = s;
    }
    
    void Personal::writeToFile(fstream& out) const {
    out.write(SSN,9);
    out.write(name,nameLen);
    out.write(city,cityLen);
    out.write(reinterpret_cast(&year),sizeof(int));
    out.write(reinterpret_cast(&salary),sizeof(int));
    }
    
    void Personal::readFromFile(fstream& in) {
    in.read(SSN,9);
    in.read(name,nameLen);
    in.read(city,cityLen);
    in.read(reinterpret_cast(&year),sizeof(int));
    in.read(reinterpret_cast(&salary),sizeof(int));
    }
    
    void Personal::readKey() {
    char s[80];
    cout << "Enter SSN: ";
    cin.getline(s,80);
    strncpy(SSN,s,9);
    }
    
    ostream& Personal::writeLegibly(ostream& out) {
    SSN[9] = name[nameLen] = city[cityLen] = '\0';
    out << "SSN = " << SSN << ", name = " << name
    << ", city = " << city << ", year = " << year
    << ", salary = " << salary;
    return out;
    }
    
    istream& Personal::readFromConsole(istream& in) {
    char s[80];
    cout << "SSN: ";
    in.getline(s,80);
    strncpy(SSN,s,9);
    cout<<'['<<SSN<<']';
    cout << "Name: ";
    in.getline(s,80);
    strncpy(name,s,nameLen);
    cout<<'['<<name<<']';
    cout << "City: ";
    in.getline(s,80);
    strncpy(city,s,cityLen);
    cout<<'['<<city<<']';
    cout << "Birthyear: ";
    in >> year;
    cout<<'['<<year<<']';
    cout << "Salary: ";
    in >> salary;
    cout<<'['<<salary<<']';
    cin.ignore();
    return in;
    }
    **************************** student.h *********************
    
    #ifndef STUDENT
    #define STUDENT
    
    #include "personal.h"
    
    class Student : public Personal {
    public:
    Student();
    Student(char*,char*,char*,int,long,char*);
    void writeToFile(fstream&) const;
    void readFromFile(fstream&);
    int size() const {
    return Personal::size() + majorLen;
    }
    protected:
    char *major;
    const int majorLen;
    ostream& writeLegibly(ostream&);
    friend ostream& operator<<(ostream& out, Student& sr) {
    return sr.writeLegibly(out);
    }
    istream& readFromConsole(istream&);
    friend istream& operator>>(istream& in, Student& sr) {
    return sr.readFromConsole(in);
    }
    };
    
    #endif
    ******************************** student.cpp ********************
    
    #include 
    #include "student.h"
    
    Student::Student() : majorLen(10) {
    Personal();
    major = new char[majorLen+1];
    }
    
    Student::Student(char ........n, char *n, char *c, int y, long s, char *m) :
    majorLen(11) {
    Personal(ssn,n,c,y,s);
    major = new char[majorLen+1];
    strcpy(major,m);
    }
    
    void Student::writeToFile(fstream& out) const {
    Personal::writeToFile(out);
    out.write(major,majorLen);
    }
    
    void Student::readFromFile(fstream& in) {
    Personal::readFromFile(in);
    in.read(major,majorLen);
    }
    
    ostream& Student::writeLegibly(ostream& out) {
    Personal::writeLegibly(out);
    major[majorLen] = '\0';
    out << ", major = " << major;
    return out;
    }
    
    istream& Student::readFromConsole(istream& in) {
    Personal::readFromConsole(in);
    char s[80];
    cout << "Major: ";
    in.getline(s,80);
    strncpy(major,s,9);
    return in;
    }
    ***************************** database.h ************************
    #ifndef DATABASE
    #define DATABASE
    
    template
    class Database {
    public:
    Database();
    void run();
    private:
    fstream database;
    char fName[20];
    ostream& print(ostream&);
    void add(T&);
    bool find(const T&);
    void modify(const T&);
    friend ostream& operator<<(ostream& out, Database& db) {
    return db.print(out);
    }
    };
    
    #endif
    *********************** database.cpp *************************
    #include 
    #include "personal.h"
    #include "student.h"
    #include "database.h"
    
    template
    Database::Database() {
    }
    
    template
    void Database::add(T& d) {
    database.open(fName,ios::in|ios::out|ios::binary);
    database.seekp(0,ios::end);
    d.writeToFile(database);
    database.close();
    }
    
    template
    void Database::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
    bool Database::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
    ostream& Database::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
    void Database::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().run();
    // Database().run();
    return 0;
    }
    Last edited by Salem; 07-29-2006 at 04:10 PM. Reason: Added code tags, but it still lacks indentation. The OP should fix it

  2. #2
    pwns nooblars
    Join Date
    Oct 2005
    Location
    Portland, Or
    Posts
    1,094
    [code][/code] too hard to read without indentation.

  3. #3
    The larch
    Join Date
    May 2006
    Posts
    3,573
    In main, I think you might need an actual Database object.

    Code:
    int main() {
        Database myDataBase;
        myDataBase.run();
        return 0;
    }
    As for the rest, using STL strings and containers usually makes things easier...

  4. #4
    Registered User
    Join Date
    May 2006
    Posts
    903
    Many things are way off. For example, you use template instead of template <typename T> or template <class T>. Also, you define templated classes and functions inside an implementation file (.cpp) which is illegal. Templated classes/structs/functions should be declared and implemented in a header file. I think it's valid to have two separate header files though. You could have my_templated_class_header.h and my_templated_class_impl.h and then include my_templated_class_impl.h in my_templated_class_header.h. There's also a definite lack of indentation and comments which makes your code harder to read. Also, while we're there, you use dynamic memory allocation and C-string functions over std::string which is quite pointless. std::string will make you save a lot of time and hassle.

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