How to pass null pointer to Win32 API in C# .Net?

Question

I'm looking at the RegisterHotKey Function:

http://msdn.microsoft.com/en-us/library/ms646309(VS.85).aspx

BOOL RegisterHotKey(
  __in  HWND hWnd,
  __in  int id,
  __in  UINT fsModifiers,
  __in  UINT vk
);

I've been using IntPtr to pass in the first argument, which works fine in most cases. But now I need to deliberately pass a null pointer as the first argument, which IntPtr (deliberately) will not do. I'm new to .Net, and this has me perplexed. How can I do this?

Other ways to pass the first argument: stackoverflow.com/questions/47997942/… — River
– River, Commented Dec 28, 2017 at 22:53

JaredPar · Accepted Answer · 2010-03-24 17:34:28Z

20

Use IntPtr.Zero for NULL

For example:

public void Example() {
  ...
  RegisterHotKey(IntPtr.Zero, id, mod, vk);
}

[DllImportAttribute("user32.dll", EntryPoint="RegisterHotKey")]
[return: MarshalAsAttribute(System.Runtime.InteropServices.UnmanagedType.Bool)]
public static extern bool RegisterHotKey(
  IntPtr hWnd, 
  int id, 
  uint fsModifiers, 
  uint vk);

answered Mar 24, 2010 at 17:34

JaredPar

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2 Comments

Thom Smith Over a year ago

Ah, I was under the impression that IntPtr.Zero represented a non-null pointer to an integer value of 0.

JaredPar Over a year ago

@Thom, IntPtr.Zero is a pointer with the address of 0. It actually points to nothing because dereferencing the address 0 will almost certainly lead to a crash or exception of sorts. The C++ value NULL has the same behavior (pointer with address of 0) hence it matches nicely with IntPtr.Zero

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