CODEWITHSUNDEEP
c++arraysclasspointersfstream
Kareem Youssef
Kareem Youssef

Reputation: 37

Reading values from a file and using classes

Hi I'm having trouble with filling the values of 2 private class members from an input file which is called money.txt . Can you please tell me why it only reads the first value of the file (after the size which is declared on the first line) and then doesn't read the rest of the values? If my method isn't the best approach can you recommend another method to solve this ?

Here is the money.h file:

#ifndef money_h
#define money_h
class Money{
public:
    void getdollars();
    void getcents();
    void printdollars();
    void printcents();
private:
    int dollars[3];
    int cents[3];
};
#endif

Here's the implementation.cpp

#include"money.h"
#include<fstream>
#include<iostream>
using namespace std;
    ifstream instream;
void Money::getdollars()
{
    instream.open("money.txt");
    int s;
    instream>>s;
    instream>>dollars[0];
    instream>>dollars[1];
    instream>>dollars[2];
}
void Money:: getcents()
{
    instream.open("money.txt");
    int s;  
    instream>>s;
    instream>>cents[0];
    instream>>cents[1];
    instream>>cents[2];
}
void Money:: printdollars()
{
    cout<<*dollars;
}
void Money:: printcents()
{
    cout<<*cents;
}

Here are the main.cpp and money.txt files

#include"money.h"
#include<iostream>
#include<fstream>
using namespace std;

Money** readMoney(Money** &x , char* filename)
{
    int size;
    ifstream instream;
    instream.open(filename);
    instream>>size;
    x = new Money*[size];
    for(int i = 0;i<size;i++)
    {
        x[i] = new Money[size];
        for(int j = 0;j<size;j++)
        {
        x[i][j].getdollars();
        x[i][j].getcents();
        }
    }
    return x;

}
void printmoney(Money **a,int size)
{
    ifstream instream;
    int i = 0 , j = 0;
    while(i<size && j<size)
    {
    a[i][j].printdollars();
    cout<<" ";
    a[i][j].printcents();
    cout<<endl;
    j++;
    }
}
void main()
{
    Money** test;
    ifstream instream;
    readMoney(test,"money.txt");
    printmoney(test,3);
}

Money.txt

3
5 60
2 30
3 21

Upvotes: 1

Views: 1823

Answers (2)

doctorlove
doctorlove

Reputation: 19282

When you open a file, it starts reading from the beginning by default.

You can seek to other places, but this is not needed in your case.

If you make the ifstream instream; a member of the class, and pass in the filename, it can open the file in the constructor and deserialise there. (Or in you get functions if you must).

Otherwise you could open the file in main and let the get functions take a input stream.

Either way open the file once and allow each read to leave the next read point ready for you.

Edit:

Just as an example, if you send the stream into the get functions as something more general, like istream this allows you to send in stringstream or other stream types.

void Money::getdollars(istream &file)
{
    int s;  
    file>>s;
    file>>dollars[0];
    file>>dollars[1];
    file>>dollars[2];
}
//... and similarly for other functions
//...
#include "money.h"
#include <sstream>

int main()
{
    Money money;
    std::stringstream stream("3\n5 60\n2 30\n3 21");
    money.getdollars(stream);
}

Note taking it by reference istream &file so the state can change.

Upvotes: 1

Aleksei Fedotov
Aleksei Fedotov

Reputation: 404

From a quick look it seems that the code opens the file "money.txt" three times. The first time in the function readMoney, the second time in getdollars and the third time in getcents. Probably this the problem. Open the file only once in readMoney function and pass the opened stream to the instance of Money.

Upvotes: 3

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