Print vector of coordinates obtained from a text file in a specific format in C++

Question

The following is the code that I am working on -

#include <iostream>
#include <algorithm>
#include <vector>
#include <fstream>
#include <iterator>

using namespace std;

struct coord {
long x,y;
};

int main()
{
ifstream nos("numbers.txt");
vector< long > values;
double val;
while ( nos >> val )
{
    values.push_back(val);
}

copy(values.begin(), values.end(), ostream_iterator<double>(cout, "\n" ));
return 0;

}

I understand the initial struct is not necessary here, but I wish to use that. I want my input text file to be something like this -

1,2
2,3
4,5

I then use my program, to input these numbers into a vector and print out that vector in the same format

Could anyone tell me what's the correct way of doing so?

I have referred to the following for the code, but I need to read and print out in the format mentioned above and I am not sure what's the best way to proceed.

For better clarity - I am attempting to implement a convex hull algorithm. I am trying to get better at programming at the same time and hence such a jump.

Answer 1

Question: Why are you mixing double and long? I'll assume you want to use long throughout the code. The easiest way to do what you want is to add a dummy variable that reads the , between the numbers:

int main()
{
ifstream nos("numbers.txt");
vector< long > values;
long val1, val2;
char dummy;
while ( nos >> val1 >> dummy >> val2)
{
    values.push_back(val1);
    values.push_back(val2);
}

copy(values.begin(), values.end(), ostream_iterator<long>(cout, "\n" ));
}

Also, you defined a struct named coord, but you don't use it in the code. If you would like to use that, you could use the following code:

std::ostream& operator<<(std::ostream& os, const coord& c)
{
    os << c.x << " " << c.y;
    return os;
}

int main()
{
ifstream nos("numbers.txt");
vector< coord > values;
coord c;
char dummy;
while ( nos >> c.x >> dummy >> c.y )
{
    values.push_back(c);
}

copy(values.begin(), values.end(), ostream_iterator<coord>(cout, "\n" ));
}

Also, in C++11 you could change the code to:

long x, y;
char dummy;
while ( nos >> x >> dummy >> y )
{
    values.emplace_back(coord{x, y});
}

Or you could also look into std::pair<long, long> for placing your coordinates in.

Answer 2

It may be a little overkill for something this simple, but I would overload the ostream and istream output and input operators, respectively.

EDIT: I guess since a struct has default public variables you don't need the friend class, but I'll keep it in, as it is the common practice for overloading << and >>

struct coord {
    long x,y;

    friend class ostream;
    friend class istream;
};

istream& operator>>( istream& is, coord& c )
{
     char comma;
     return is >> c.x >> comma >> c.y;
}

ostream& operator<<( ostream& os, const coord& c )
{
     char comma = ',';
     return os << c.x << comma << c.y;
}

int main()
{
    ifstream nos("numbers.txt");
    vector< coord > values;

    coord val;
    while ( nos >> val )
        values.push_back(val);

    for each( value : values )
        cout << value << endl;

    return 0;
}