SFML C++ why is nothing drawn on screen here? (simple code) - c++

Question

Here is my example program using SFML library in C++. I want to create a custom function 'draw_func' which draws something (like a rectangle in this example) at provided coordinates. I set the type of the return variable as an sfml object rectangle (which is what I return and what I draw) but the screen is black.
#include <iostream>
#include <math.h>
#include "SFML/OpenGL.hpp"
#include <SFML/Graphics.hpp>
sf::RectangleShape draw_func(int x, int y)
{
sf::RectangleShape rect(sf::Vector2f(200, 100));
rect.setPosition(x, y);
rect.setFillColor(sf::Color((0, 0, 255)));
return rect;
}
int main()
{
int height = 400;
int length = 400;
int pos_x = 0;
int pos_y = 0;
sf::RenderWindow window(sf::VideoMode(length, height), "My window");
while (window.isOpen())
{
sf::Event event;
while (window.pollEvent(event))
{
if (event.type == sf::Event::Closed)
window.close();
}
window.clear(sf::Color::Black);
sf::RectangleShape rectangle = draw_func(pos_x, pos_y);
window.draw(rectangle);
window.display();
}
}

Answer 1

I think the problem is with this statemen here:
rect.setFillColor(sf::Color((0, 0, 255)));
The double parentheses actually resolves to a single value, 0 because:
sf::Color((0, 0, 255))
constructs a sf::Color with the value 0 because
(0, 0, 255)
is not function parameters because of the extra parentheses it is an expression involving the comma operator:
0, 0, 255
The comma operator always has the value of its left most expression. In this case 0.
Now sf::Color has a constructor that takes a single value:
sf::Color(Uint32 color);
You are creating black sf::Color(0).