C++ 2D Vectors

What Will You Learn in This Guide?

This guide teaches you how to create 2D Vectors using the C++ Standard Template Library (STL).
Unlike arrays, 2D vectors have dynamic dimensions, so data can be added, deleted, and resized at runtime.
It is ideal for high-performance data management in matrix, table or graph structures.

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2D Vector Concept

A 2D vector is actually a vector of vectors.
Each row (vector<int>) is a vector on its own, and the outer vector contains them:

vector<vector<int>> tablo {{1, 2, 3}, {4, 5}, {6, 7, 8}};

• Note: Lines can be of different lengths; This structure is called “jagged array”.

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1. Required Libraries

To use vectors in C++, include this header file:

#include <vector>
Tüm STL kütüphanelerini tek seferde dahil etmek isterseniz:


#include <bits/stdc++.h>

2. Creating and Initializing 2D Vector

1. Static Initialization (While Values Are Known)

If you know your values beforehand, you can initialize it directly:

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

int main() {
    vector<vector<int>> matris {{10, 20, 30}, {40, 50}, {60, 70, 80}};
    
    for (int i = 0; i < matris.size(); i++) {
        for (int j = 0; j < matris[i].size(); j++)
            cout << matris[i][j] << " ";
        cout << endl;
    }
}

Çıktı:

10 20 30
40 50
60 70 80

2. Starting by Specifying a Size

To know the number of rows/columns and initialize all elements with the same value:

int satir = 4, sutun = 3;
vector<vector<int>> tablo(satir, vector<int>(sutun, 0));

Çıktı:


0 0 0
0 0 0
0 0 0
0 0 0

• vector<int>(sutun, 0) → creates 3 columns for each row, assigns 0 to all cells. table(row, …) → repeats this structure as 4 rows.

3. Blank 2D Vector

If you want to add data dynamically you can create empty:

vector<vector<int>> tablo;

3. Navigating 2D Vector

With For Loop

for (int i = 0; i < tablo.size(); i++) {
    for (int j = 0; j < tablo[i].size(); j++)
        cout << tablo[i][j] << " ";
    cout << endl;
}

With Iterator:

vector<vector<int>> tablo {{1, 0, 1}, {0, 1}, {1, 0, 1}};
vector<vector<int>>::iterator itSatir;
vector<int>::iterator itSutun;

for (itSatir = tablo.begin(); itSatir != tablo.end(); itSatir++) {
    for (itSutun = itSatir->begin(); itSutun != itSatir->end(); itSutun++)
        cout << *itSutun << " ";
    cout << endl;
}

• begin() → starting iterator end() → iterator pointing after

4. Adding Elements to a 2D Vector

push_back() – Add New Line

vector<vector<int>> v;
v.push_back({10, 0, 10});
v.push_back({0, 5});
v.push_back({7, 8, 9});

Çıktı:


10 0 10
0 5
7 8 9

insert() – Insert at Specific Position

auto it = v.begin();
v.insert(it + 1, {1, 2, 3}); // 2. satıra ekler

Çıktı:


10 0 10
1 2 3
0 5
7 8 9

• The insert() function takes an iterator, not an index.

5. Delete Element

pop_back() – Delete Last Line

v.pop_back();

erase() – Delete Specific Row

v.erase(v.begin() + 1);

clear() – Clear All

v.clear();

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Technical Specifications Table

Feature	Description
Data Structure	vector<vector<T>> (nested dynamic structure)
Default Initialization	vector<vector<int>>(satir, vector<int>(sutun, 0))
Adding Functions	push_back(), insert()
Delete Functions	pop_back(), erase(), clear()
Roaming	Nested loop for or iterator
Time Complexity	O(N × M) (row × column)
Scope	Matrix, graph, table data structures

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Frequently Asked Questions (FAQ)

1. Why use 2D Vector instead of 2D Array?

Because vectors are dynamic, arrays are fixed size. You can change the size, add and delete data while the program is running.

2. Can lines be of different lengths?

Yes. Each interior vector is independent and can have a different number of columns.

3. Can I add a single number to a 2D vector?

No, it can only be added to the subvector (v[i].push_back(x)).

4. How do I learn the capacity of 2D vectors?

v.size() → number of rows, v[i].size() → number of columns.

5. Does clear() completely clear memory?

No, it preserves the capacity but removes the elements.

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Result

It is one of the most flexible solutions for working with multidimensional data such as 2D vectors, matrix, graph and tabular structures in C++. It is much more dynamic and secure than fixed size arrays.

You can try it immediately on the GenixNode platform to test this structure in your own applications.