How to create a 2D vector in C++

What is a vector in C++?

A vector in C++ is a sequence of containers that represent an array but with the added ability to adjust its size during runtime. The elements in a vector are stored in linear memory locations, which allow for efficient access to any element.

To use the vectors in our program, we use the C++ STL vector library. This library offers a variety of techniques for manipulating and efficiently accessing the elements in the container.

2D vector in C++

To declare a 1D vector, we use the following format:

vector<datatype> variable_name

When working with a 2D vector in C++, we can create it by defining a vector of data type vector. To do this, we will replace datatype with vector<datatype> and declare a variable using the following syntax:

vector<vector<datatype>> variable_name;

Note: Please replace datatype with actual data type names such as int, double, etc.

Coding example

Let’s write code for 2D vectors with the dimensions 3x3 below:

#include <iostream>
#include <vector>
using namespace std;
int main()
{
	vector<vector<int>> Arr
	{
		{0, 1, 2},  // Row 0 has 1,2,3
		{3, 4, 5},  // Row 1 has 4,5,6
		{6, 7, 8}   // Row 2 has 7,8,9
	};
	for (int i = 0; i < Arr.size(); i++) // Arr.size() will return a size of vector which is 3
	{
		for (int j = 0; j < Arr.size(); j++) 
		{
			cout << Arr[i][j] << " ";
		}	
		cout << endl;
	}
	return 0;
}

Explanation

  • Lines 7–12: We initialize the 2D vector with the name Arr and dimensions 3x3.

  • Lines 13–20: We use a nested loop to display the vector’s elements on the console.

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