DynamicArrays.md

Dynamic Arrays (std::vector)

Video

#include <string>
#include <iostream>
#include <vector>

struct Vertex
{
    float x, y, z;
};

std::ostream& operator<<(std::ostream& stream, const Vertex& vertex)
{
    stream << vertex.x << ", " << vertex.y << ", " << vertex.z;
    return stream;
}

void NormalizeVertices(std::vector<Vertex>& vertices)
{
    for (Vertex& v : vertices)
    {
        double const magnitude = std::sqrt(v.x * v.x + v.y * v.y + v.z * v.z);
        v.x /= magnitude;
        v.y /= magnitude;
        v.z /= magnitude;
    }
}

int main()
{	
    std::vector<Vertex> vertices;
    vertices.push_back({ 1, 2, 3 });
    vertices.push_back({ 4, 5, 6});

    for (int i = 0; i< vertices.size(); i++)
    {
        std::cout << vertices[i] << std::endl;
    }

    NormalizeVertices(vertices);

    // Here we copy the vertex inside the scope of the for-loop
    for (Vertex v : vertices)
    {
        std::cout << v << std::endl;
    }

    // To avoid copying, we just use a reference to that Vertex
    for (Vertex& v : vertices)
    {
        std::cout << v << std::endl;
    }

    vertices.clear();

    std::cin.get();
}

Optimizing the usage of std::vector

Video

#include <iostream>
#include <vector>

struct Vertex
{
public:
    float x, y, z;

    Vertex(float x, float y, float z)
        : x(x), y(y), z(z)
    {
    }

    Vertex(const Vertex& vertex)
        :x(vertex.x), y(vertex.y), z(vertex.z)
    {	
        std::cout << "Copied!" << std::endl;
    }
};

int main()
{	
    // This code produces six copies
    std::vector<Vertex> vertices;
    vertices.push_back(Vertex(1, 2, 3));
    vertices.push_back(Vertex(4, 5, 6));
    vertices.push_back(Vertex(7, 8, 9));

    std::cin.get();
}

Two easy optimizations
1st - We reserve the memory for the expect number of elements
2nd - We instantiate our objects in place std::vector.emplace_back()

int main()
{		
    std::vector<Vertex> vertices;
    // 1st optimization
    vertices.reserve(3);

    // 2nd optmization
    vertices.emplace_back(1, 2, 3);
    vertices.emplace_back(4, 5, 6);
    vertices.emplace_back(7, 8, 9);

    std::cin.get();
}