c - win32 api rectangle is not drawn if hdc passed to method - c

Question

I have been playing with C and win32 recently and the following has me balked:
case WM_PAINT:
g_crntRect = (RECT*) malloc(sizeof(RECT));
GetWindowRect(hwnd, g_crntRect);
hpen = CreatePen(PS_SOLID, 1, RGB(255,25,5));
hdc = BeginPaint (hwnd, &ps) ;
oldPen = SelectObject(hdc, hpen);
drawRects(hwnd, hdc);
//Rectangle(hdc, 0, 0, 840, 525);
SelectObject(hdc,oldPen);
DeleteObject(hpen);
EndPaint (hwnd, &ps) ;
return 0 ;
So, if I call my own method above for drawing rectangles, it draws nothing, however the call to draw the rectangle in the WM_PAINT that I have commented above succeeds without a problem.
Here is my method:
BOOL drawRects(HWND hwnd, HDC hdc)
{
char buffer[50];
BOOL res = FALSE;
RECT tempRect = {0};
char quadStr[6] = "";
int i = 0;
quadStr[i]='*';
OutputDebugString("Going to draw");
for (i = 1; i <= 4; i++)
{
//get rect for each quadrent from the parent
OutputDebugString("inside for");
getRect(g_crntRect, &tempRect, i);
OutputDebugString("got rectr");;
res = Rectangle(hdc, tempRect.right, tempRect.top, tempRect.right, tempRect.bottom);
if (res == FALSE)
{
OutputDebugString("false");;
sprintf(buffer, "Error: %ld", GetLastError());
OutputDebugString(buffer);
}
else
{
OutputDebugString("drew");;
}
quadStr[i]='*';
printRect(quadStr, &tempRect);
}
return TRUE;
}
Looking at debug output, everything seems fine. Proper values are being passed into the Rectangle method. However, I wonder if I am not passing HDC correctly?
Any ideas?

Answer 1

Looks like a simple typo. In your method you have:
res = Rectangle(hdc, tempRect.right, tempRect.top, tempRect.right, tempRect.bottom);
The second parameter should be tempRect.left not tempRect.right. You're trying to draw a zero-width rectangle.

Answer 2

Change
BOOL drawRects(HWND hwnd, HDC* hdc)
to
BOOL drawRects(HWND hwnd, HDC hdc)
A Windows handle is actually a pointer, so there is no need to pass it by reference. But if you do, you would need to call your function as drawRects(hwnd, &hdc);

Answer 3

In general you don't paint outside the WM_PAINT handler. If you want your window to be updated, just call InvalidateRect on the area you want to be redrawn. That will trigger the WM_PAINT call which will then repaint the window.
Is there a reason you need to paint the window outside the paint handler?