Using a screen capture without saving to disk in c++ - c++

Question

I am attempting to capture images from the screen. I currently have code which takes a screenshot and saves it to disk but I would prefer to not save it each time. After several hours of reading over other examples online I still feel I do not understand how this process works.
The two goals are to create the screen in memory to be passed to another function and to be able to capture only selected parts of the screen given (x,y) coordinates.
I am relatively new to coding so if this is a trivial thing it would not surprised but would still greatly appreciate any explanations.
Here is the sample code I found online and have been working with.
#define _CRT_SECURE_NO_DEPRECATE
#include <iostream>
#include <windows.h>
#include <stdio.h>
#include <string>
using namespace std;
void ScreenShot()
{
int nScreenWidth = GetSystemMetrics(SM_CXSCREEN);
int nScreenHeight = GetSystemMetrics(SM_CYSCREEN);
HWND hDesktopWnd = GetDesktopWindow();
HDC hDesktopDC = GetDC(hDesktopWnd);
HDC hCaptureDC = CreateCompatibleDC(hDesktopDC);
HBITMAP hCaptureBitmap = CreateCompatibleBitmap(hDesktopDC,
nScreenWidth, nScreenHeight);
SelectObject(hCaptureDC, hCaptureBitmap);
BitBlt(hCaptureDC, 0, 0, nScreenWidth, nScreenHeight,
hDesktopDC, 0, 0, SRCCOPY | CAPTUREBLT);
//SaveCapturedBitmap(hCaptureBitmap); //Place holder - Put your code here to save the captured image to disk
ReleaseDC(hDesktopWnd, hDesktopDC);
DeleteDC(hCaptureDC);
DeleteObject(hCaptureBitmap);
}