Question

I’m converting a C++ application in C# and managing to work my way through most of it. However I’m stuck with the following statement:

#define GET_SHCALL_ID(L)                           (((L) >> 24) & 0x000000FF)

It’s called by another part of the application that receives a Window Message and is passing in the lParam to this call, as shown below:

// We perform and event handling to display state as required here..
LRESULT CShockSampleDlg::OnShockCallEvent(WPARAM wParam, LPARAM lParam)
{
  // Pass events here so that they will be displayed int the m_LogMessages window.
  OnDebugCallEvents(wParam, lParam);

  UINT callID = GET_SHCALL_ID(lParam);
  UINT chanID = GET_SHCHAN_ID(lParam);
  UINT info   = GET_SHCHAN_INFO(lParam);

So my questions are:

• What is the macro/method doing?
• What would be the equivalent in C#?

Answer 1

Consider that 32-bit integer be composed of 4 octets (bytes):

  zzyyxxww
0x12345678

That operations extracts the “zz” (0x12) byte.

But that’s just the implementation. The usage is clearly written in the name GET_SHCALL_ID — It gets the shock call ID from the lParam.

C# and C++ share many operators, in this case the function is just the same.

uint GET_SHCALL_ID(uint lParam) { return (lParam >> 24) & 0xFF; }