Thread: Define a function

I do not know where to start with this requirement. I know I have to int isNull() and write it to a file, but not really know how to const it.

Just need an example on how to start this, thanks

Need to define function isNull() in personal class and define function writeNullToFile to overwrite a record to be deleted by a null record. The null record is defined as having a nonnumeric character (a tombstone) in the first position of the SSN member.

Code:

#include <iostream>
#include <fstream>
#include <cstring>

using namespace std;

#ifndef PERSONAL
#define PERSONAL

class Personal 
{
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 strncmp(pr.SSN,SSN,9) == 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







#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<const char*>(&year),sizeof(int));
    out.write(reinterpret_cast<const char*>(&salary),sizeof(int));
}

void Personal::readFromFile(fstream& in) 
{
    in.read(SSN,9);
    in.read(name,nameLen);
    in.read(city,cityLen);
    in.read(reinterpret_cast<char*>(&year),sizeof(int));
    in.read(reinterpret_cast<char*>(&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 << "Name: ";
    in.getline(s,80);
    strncpy(name,s,nameLen);
    cout << "City: ";
    in.getline(s,80);
    strncpy(city,s,cityLen);
    cout << "Birthyear: ";
    in >> year;
    cout << "Salary: ";
    in >> salary;
    in.getline(s,80); // get '\n'
    return in;
}

I am having a problem defining the method within the class.

Which method? This one?

define function writeNullToFile to overwrite a record to be deleted by a null record

It doesn't make sense for Personal to overwrite any records in a file.

If you insist so, the signature might be:

Code:

void Personal::writeNullToFile(fstream&, int where, int howManyBytes);

Write any data to this place, but change the first character of SSN to a non-number before writing it to file.

The isNull method would simply return, if the first character of SSN is non-numeric.

The isNull method, how would I start the int.

int isNull()

int a

if (isNull() = a)

wruteNullTo File