Segmentation Issue RW

[NDP286]

..

[bbgst]

On your first lines of main, you are creating a vector of pointers to Atom objects, but you're not creating those objects:

vector<vector<Atom *> > position(duration, vector<Atom *>(particles));

So, inside the for loop, you get segfault the first time you do

position[0][i]->_x = count;

[ne555]

[code] "Please use code tags" [/code]

//vector<vector<Atom *> > position(duration,vector<Atom *>(particles));
vector<vector<Atom> > position(duration,vector<Atom>(particles));

//int* Atom = new int[particles];
vector<int> Atom(particles);

[NDP286]

Yes you are right bbgst, I need to create objects. But i dont know how to do, please help me in this issue. I need this one

[bbgst]

You could either use ne555's solution and use local objects or use

Edit: this is wrong, sorry.

vector<vector<Atom *>> position(duration, vector<Atom>(particles, new Atom));

[ne555]

That is no good. vector<Atom>(particles, new Atom) is using the copy constructor, so all the pointers point to the same address.

[bbgst]

Oops, that's what you get when you quick-reply.

[NDP286]

So what can i do now, my homework needs to use vectors and dynamic memory management (new and delete operators) and i dont know how to proceed with, please help me in this issue

[bbgst]

First of all, code tags and indentation.

#include <iostream>
#include <cstdlib>
#include <fstream>
#include <vector>
using namespace std;

int DefineDuration()
{
	int durations;
	cout<<"Enter the Duration:";
	cin>>durations;
	return durations;
}

int DefineParticles()
{
	int particle;
	cout<<"Enter the Particles:";
	cin>>particle;
	return particle;
}

class Atom
{
	public:
		int _x;
		int _y;
};

int main()
{
	int duration = DefineDuration();
	int particles= DefineParticles();
	vector<vector<Atom *> > position(duration,vector<Atom *>(particles));

	int* Atom = new int[particles];
	int count=1;
	for (int i=0; i<particles; i++)
	{
		position[0][i]->_x=count;
		position[0][i]->_y=count;
		count++;
	}

	srand(time(0));
	int displacement=1;

	for (int t=1; t<duration; t++)
	{
		for (int j=0; j<particles; j++)
		{
			switch (rand()%4)
			{
				case 0:
					position[t][j]->_x = position[t-1][j]->_x + displacement;
					position[t][j]->_y = position[t-1][j+1]->_y + displacement;
					break;

				case 1:
					position[t][j]->_x = position[t-1][j]->_x - displacement;
					position[t][j]->_y = position[t-1][j+1]->_y - displacement;
					break;

				case 2:
					position[t][j]->_x = position[t-1][j]->_x + displacement;
					position[t][j]->_y = position[t-1][j+1]->_y + displacement;
					break;

				case 3:
					position[t][j]->_x = position[t-1][j]->_x - displacement;
					position[t][j]->_y = position[t-1][j+1]->_y - displacement;
					break;
			}
		}
	}

	ofstream myfile;
	myfile.open ("random.txt");
	for (int t=0; t<duration; t++)
	{
		for (unsigned j=0; j<position[t].size(); ++j)
			myfile << position[t][j]->_x << "," << position[t][j]->_y << " ";
		myfile << endl;
	}

	myfile.close();
	delete [] Atom;
	return 0;
}

[NDP286]

..

[bbgst]

Line 34

vector<vector<Atom *> > position(duration,vector<Atom *>(particles, (Atom *) 0));

Line 36

int * Atom = new int[particles]; // why is this necessary? 

Line 38

for (int t=0; t<duration; t++)
	for (int j=0; j<particles; j++)
		position[t][j] = new Atom;

Line 86

	myfile.close();
	delete [] Atom;

	for (int t=0; t<duration; t++)
		for (int j=0; j<particles; j++)
			delete position[t][j];

But that won't work because:
1) you created a int * Atom, which obscures the class declared outside.
2) on your loop, you are accessing the [j + 1] element on all elements, including the last, which results in a index outside your vector (lines 56, 61, 66, 71).

And more importantly, if you don't know how to do it, you should learn, not ask for the code. Showing you the code doesn't help.

[bbgst]

What I mean is if you surround your code with code tags ([ code][/code] or the first button on the left when you are posting), it keeps the formatting, making it A LOT easier to read.