GDI: must case returnvalue of SelectObject

[temuhin]

Dear Folks,

I have a small problem using the SelectObject function in GDI. The code won´t compile unless I explicitly cast the returnvalue of SelectObject to HPEN.
According to the MSDN documentation, the function returns an HGDIOBJ object and casting should not be necessary.

Any reason for this? Did I do anything wrong?

	HPEN green_pen = CreatePen(PS_SOLID,1,RGB(0,255,0));
	HPEN old_pen;
	old_pen = (HPEN)SelectObject( hdc, green_pen);
	MoveToEx(hdc,10,10,NULL);

I have included the complete code below, however, the codesnippet above should suffice.

Regards
t

// include the basic windows header file
#include <windows.h>
#include <windowsx.h>
#include <math.h>
#include <iostream>
#include <fstream>
#include <string>

#define PI 3.1415

using namespace std;

#define KEYDOWN(vk_code) ((GetAsyncKeyState(vk_code) & 0x8000) ? 1:0)
#define KEYUP(vk_code) ((GetAsyncKeyState(vk_code) & 0x8000) ? 1:0)

// the WindowProc function prototype
LRESULT CALLBACK WindowProc(HWND hWnd,
                         UINT message,
                         WPARAM wParam,
                         LPARAM lParam);

HDC hdc;
ofstream output;

// the entry point for any Windows program
int WINAPI WinMain(HINSTANCE hInstance,
                   HINSTANCE hPrevInstance,
                   LPSTR lpCmdLine,
                   int nCmdShow)
{
    // the handle for the window, filled by a function
    HWND hWnd;
	
	COLORREF red = RGB(255,0,0);
	COLORREF green = RGB(0,255,0);
	COLORREF blue = RGB(0,0,255);

    // this struct holds information for the window class
    WNDCLASSEX wc;

    // clear out the window class for use
    ZeroMemory(&wc, sizeof(WNDCLASSEX));

    // fill in the struct with the needed information
    wc.cbSize = sizeof(WNDCLASSEX);
    wc.style = CS_HREDRAW | CS_VREDRAW;
    wc.lpfnWndProc = (WNDPROC)WindowProc;
    wc.hInstance = hInstance;
    wc.hCursor = LoadCursor(NULL, IDC_ARROW);
    wc.hbrBackground = (HBRUSH)COLOR_WINDOW;
    wc.lpszClassName = L"WindowClass1";

    // register the window class
    RegisterClassEx(&wc);

    // create the window and use the result as the handle
    hWnd = CreateWindowEx(NULL,
                          L"WindowClass1",    // name of the window class
                          L"Our First Windowed Program",   // title of the window
                          WS_OVERLAPPEDWINDOW,    // window style
                          300,    // x-position of the window
                          300,    // y-position of the window
                          500,    // width of the window
                          400,    // height of the window
                          NULL,    // we have no parent window, NULL
                          NULL,    // we aren't using menus, NULL
                          hInstance,    // application handle
                          NULL);    // used with multiple windows, NULL
	hdc = GetDC(hWnd);


	// create pen
	HPEN green_pen = CreatePen(PS_SOLID,1,RGB(0,255,0));
	HPEN old_pen;

	old_pen = (HPEN)SelectObject( hdc, green_pen);
	MoveToEx(hdc,10,10,NULL);

   
	
	// display the window on the screen
    ShowWindow(hWnd, nCmdShow);
	TextOut(hdc,5,5,L"test",strlen("test"));
	
    // enter the main loop:

    // this struct holds Windows event messages
    MSG msg;
	output.open("LOGG.TXT",ios::out);
	float s = cos(0.0);
	
	//output.close();
    // wait for the next message in the queue, store the result in 'msg'
    while(true)
	{
		
		if(PeekMessage(&msg, NULL, 0, 0, PM_REMOVE))
		{
			if(msg.message == WM_QUIT)
				break;
			TranslateMessage(&msg);
			DispatchMessage(&msg);
		}
		if(KEYUP(VK_LEFT))
		{
			SetTextColor(hdc,RGB(rand()%256,rand()%256,rand()%256));
			SetBkColor(hdc,RGB(0,0,0));
			SetBkMode(hdc, TRANSPARENT);

			TextOut(hdc,100,100,L"Test DEMO", strlen("Test DEMO"));
		}
		if(KEYUP(VK_DOWN))
		{
			double f=200.0;
			double T = 1/f;
			int counter=1;
			COLORREF blue = RGB(0,0,255);

			for(int i=0;i<500;i=i+5)
			{
				
				int y = (int)(100*sin(2*PI*f*i)+250);
				
				//SetPixel(hdc,i,y,blue);
				//SetPixel(hdc,i,250,blue);
				
				LineTo(hdc,i,y);
				output << counter << "\t" <<y <<"\n";
				counter++;
			}
			output.close();

		}
		
		
	}
	ReleaseDC(hWnd,hdc);
	
  
}

// this is the main message handler for the program
LRESULT CALLBACK WindowProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
	PAINTSTRUCT ps;
	
	RECT rect;
    // sort through and find what code to run for the message given
    switch(message)
    {
		case WM_CREATE:
			{
				MessageBox(NULL, L"CREATED",L"",MB_OK);
			}
			break;
		case WM_PAINT:
			{
				//hdc = GetDC(hWnd);
				//ReleaseDC(hWnd,hdc);
				GetClientRect(hWnd,&rect);
				ValidateRect(hWnd,&rect);
				return 0;
			}
			break;
        // this message is read when the window is closed
        case WM_DESTROY:
            {
                // close the application entirely
                PostQuitMessage(0);
                return 0;
            } break;
		default:
			break;
    }

    // Handle any messages the switch statement didn't
    return DefWindowProc (hWnd, message, wParam, lParam);
}