Pointers and Memory

Multidimensional Arrays

A two-dimensional built-in array is stored contiguously in row-major order in both C and C++.

What is Multidimensional Arrays?

A two-dimensional built-in array is stored contiguously in row-major order in both C and C++.

Traverse a row-major matrix and calculate row totals.

Important points

Every pointer must refer to a live compatible object or be null.
Pair each owned allocation with exactly one release.
Prefer clear ownership and const-correct interfaces.

C and C++ code examples

Run code →

main.c

#include <stdio.h>

int main(void) {
    int matrix[2][3] = {{1, 2, 3}, {4, 5, 6}};
    for (int row = 0; row < 2; ++row) {
        int total = 0;
        for (int column = 0; column < 3; ++column) total += matrix[row][column];
        printf("row %d=%d\n", row, total);
    }
    return 0;
}

Expected output

row 0=6
row 1=15

C++

Run code →

main.cpp

#include <array>
#include <iostream>

int main() {
    std::array<std::array<int, 3>, 2> matrix{{{{1, 2, 3}}, {{4, 5, 6}}}};
    for (std::size_t row = 0; row < matrix.size(); ++row) {
        int total = 0;
        for (int value : matrix[row]) total += value;
        std::cout << "row " << row << '=' << total << '\n';
    }
}

Expected output

row 0=6
row 1=15

C and C++ comparison

A C function parameter must know every dimension except the first. std::array preserves dimensions in its type and exposes bounds-aware alternatives such as at.

Ownership and cleanup are conventions enforced by the programmer.

C++

Containers and RAII types can encode ownership and cleanup in object lifetimes.

Practice exercises

Run both versions, then modify them to observe the different language guarantees.

Test null and allocation-failure paths.
Run with AddressSanitizer and UndefinedBehaviorSanitizer.
Document whether every pointer owns or only observes its object.