2D Dynamic Array Based on User Input [duplicate] - c++

Question

This question already has answers here:
Finding size of dynamically allocated array
(8 answers)
Closed 4 years ago.
Scenario:
Read numbers from file and create dynamic 2d array accordingly
The first line of data file represents the rooms and rest of the lines represent the number of person in the room
For example:
4
4
6
5
3
total 4 rooms, 1st room has 4 people, 2nd room has 6 people...
So far this is my code, how do I check I've created the dynamic array with correct size?
#include <iostream>
#include <fstream>
#include <string>
#include <sstream>
using namespace std;
int main()
{
ifstream readFirstLine("data.txt");
ifstream readData("data.txt");
string line;
int numRoom, numPerson = 0;
int i = -1;
while (getline(readFirstLine, line))
{
istringstream linestream(line);
if (i == -1)
{
linestream >> numRoom;
cout << "numRoom:" << numRoom << endl;
break;
}
}
readFirstLine.close();
int** numRoomPtr = new int*[numRoom];
while (getline(readData, line))
{
istringstream linestream(line);
if (i == -1)
{
}
else
{
linestream >> numPerson;
numRoomPtr[i] = new int[numPerson];
cout << "i:" << i << endl;
cout << "numPerson:" << numPerson<< endl;
}
i++;
}
readData.close();
return 0;
}

Answer 1

A better way to do your current program, using std::vector, could be like this:
#include <iostream>
#include <vector>
#include <fstream>
int main()
{
std::ifstream dataFile("data.txt");
// Get the number of "rooms"
unsigned roomCount;
if (!(dataFile >> roomCount))
{
// TODO: Handle error
}
// Create the vector to contain the rooms
std::vector<std::vector<int>> rooms(roomCount);
for (unsigned currentRoom = 0; currentRoom < roomCount; ++currentRoom)
{
unsigned personCount;
if (dataFile >> personCount)
{
rooms[currentRoom].resize(personCount);
}
else
{
// TODO: Handle error
}
}
// Don't need the file anymore
dataFile.close();
// Print the data
std::cout << "Number of rooms: " << rooms.size() << '\n';
for (unsigned currentRoom = 0; currentRoom < rooms.size(); ++currentRoom)
{
std::cout << "Room #" << currentRoom + 1 << ": " << rooms[currentRoom].size() << " persons\n";
}
}
As you can see, it's now possible to get the "sizes" of the data after you're done with the reading from the file.