How the Pong.cpp file know the implementation of the functions in Bat.cpp if it doesn't include Bat.cpp? [duplicate]

How the Pong.cpp file know the implementation of the functions in Bat.cpp if it doesn't include Bat.cpp? Is that magic? I want to know what's happening? I am coming from Python programming language and its obvious in Python classes because their implementation of functions come with the signatures.

Here are all the files I am working with:

Bat.h

    #pragma once
    #include <SFML/Graphics.hpp>
    using namespace sf;
    class Bat
    {
    private:
        Vector2f m_Position;
        // A RectangleShape object
        RectangleShape m_Shape;
        float m_Speed = 1000.0f;
        bool m_MovingRight = false;
        bool m_MovingLeft = false;
    public:
        Bat(float startX, float startY);
        FloatRect getPosition();
        RectangleShape getShape();
        void moveLeft();
        void moveRight();
        void stopLeft();
        void stopRight();
        void update(Time dt);
    };

Bat.cpp

    #include "Bat.h"
    
    // This is the constructor and it is called when we create an object
    Bat::Bat(float startX, float startY)
    {
        m_Position.x = startX;
        m_Position.y = startY;
    
        m_Shape.setSize(sf::Vector2f(100, 5));
        m_Shape.setPosition(m_Position);
    }
    FloatRect Bat::getPosition()
    {
        return m_Shape.getGlobalBounds();
    }
    RectangleShape Bat::getShape()
    {
        return m_Shape;
    }
    void Bat::moveLeft()
    {
        m_MovingLeft = true;
    }
    void Bat::moveRight()
    {
        m_MovingRight = true;
    }
    void Bat::stopLeft()
    {
        m_MovingLeft = false;
    }
    void Bat::stopRight()
    {
        m_MovingRight = false;
    }
    void Bat::update(Time dt)
    {
        if (m_MovingLeft)
        {
            m_Position.x -= m_Speed * dt.asSeconds();
        }
        if (m_MovingRight)
        {
            m_Position.x += m_Speed * dt.asSeconds();
        }
        m_Shape.setPosition(m_Position);
    }

Pong.cpp

#include "Bat.h"
#include <sstream>
#include <cstdlib>
#include <SFML/Graphics.hpp>
int main()
{
    // Create a video mode object
    VideoMode vm(1920, 1080);
    // Create and open a window for the game
    RenderWindow window(vm, "Pong", Style::Fullscreen);
    int score = 0;
    int lives = 3;
    
    // Create a bat at the bottom center of the screen
    Bat bat(1920 / 2, 1080 - 20);
    // We will add a ball in the next chapter
    // Create a Text object called HUD
    Text hud;
    // A cool retro-style font
    Font font;
    font.loadFromFile("fonts/DS-DIGI.ttf");
    // Set the font to our retro-style
    hud.setFont(font);
    // Make it nice and big
    hud.setCharacterSize(75);
    // Choose a color
    hud.setFillColor(Color::White);
    hud.setPosition(20, 20);
    // Here is our clock for timing everything
    Clock clock;
    while (window.isOpen())
    {
        /*
        Handle the player input
        ****************************
        ****************************
        ****************************
        */
        /*
        Update the bat, the ball and the HUD
        *****************************
        *****************************
        *****************************
        */
        
        
        /*
        Draw the bat, the ball and the HUD
        *****************************
        *****************************
        *****************************
        */
        
    }
    return 0;
}