A small snippet displaying how to get the rectangles structures (coordinates) associated with all the connected screens/monitors.

CaptureMonitorsRects.cpp

/*********************************************************************
 * \file   CaptureMonitorsRects.cpp
 * \brief  capture monitors rectangles handles in a custom structure.
 *
 * \author SuperKogito
 * \date   July 2020
 *
 * @note:
 * references and sources:
 * 
 *
 *********************************************************************/
#include <windows.h>
#include <vector>
#include <iostream>


/**
 * Structure that includes all screen hanldes and rectangles.
 */
struct cMonitorsVec
{
	std::vector<int>       iMonitors;
	std::vector<HMONITOR>  hMonitors;
	std::vector<HDC>       hdcMonitors;
	std::vector<RECT>      rcMonitors;

	static BOOL CALLBACK MonitorEnum(HMONITOR hMon, HDC hdc, LPRECT lprcMonitor, LPARAM pData)
	{
		cMonitorsVec* pThis = reinterpret_cast<cMonitorsVec*>(pData);

		pThis->hMonitors.push_back(hMon);
		pThis->hdcMonitors.push_back(hdc);
		pThis->rcMonitors.push_back(*lprcMonitor);
		pThis->iMonitors.push_back(pThis->hdcMonitors.size());
		return TRUE;
	}

	cMonitorsVec()
	{
		EnumDisplayMonitors(0, 0, MonitorEnum, (LPARAM)this);
	}
};



int main()
{
	cMonitorsVec Monitors;

	for (int monitorIndex=0;  monitorIndex < Monitors.iMonitors.size(); monitorIndex++)
	{
		std::wcout << "Screen id: " << monitorIndex << std::endl;
		std::wcout << "-----------------------------------------------------" << std::endl;
		std::wcout << " - screen left-top corner coordinates : (" << Monitors.rcMonitors[monitorIndex].left 
								   << "," << Monitors.rcMonitors[monitorIndex].top 
			                                           << ")" << std::endl;
		std::wcout << " - screen dimensions (width x height) : (" << std::abs(Monitors.rcMonitors[monitorIndex].right - Monitors.rcMonitors[monitorIndex].left) 
								   << "," << std::abs(Monitors.rcMonitors[monitorIndex].top - Monitors.rcMonitors[monitorIndex].bottom)
								   << ")" << std::endl;
		std::wcout << "-----------------------------------------------------" << std::endl;
	}
}