How to create a geometry_msgs::Point?

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I'm using ROS melodic.

I'm trying this C++ code:

#include "ros/ros.h"
#include "geometry_msgs/Twist.h"
#include "geometry_msgs/Quaternion.h"
#include "tf/transform_datatypes.h"
#include "tf/LinearMath/Matrix3x3.h"
#include "nav_msgs/Odometry.h"

#include <sstream>
#include <cmath>
#include <cstdlib>
#include <queue>

// ... More code

geometry_msgs::Point p;

But I get the following error message:

no instance of constructor "geometry_msgs::Point_::Point_ [with ContainerAllocator=std::allocator]" matches the argument list -- argument types are: (double, double)

What am I doing wrong?