How can I convert IntPtr to UIntPtr?

Question

I tried casting it like so:

UIntPtr x = (UIntPtr)intPtr;

... but the Compiler is not very happy with it and returned a compile error.

I need to do the conversion because the P/Invoke signature for RegOpenKeyEx requires a UIntPtr:

  [DllImport("advapi32.dll", CharSet = CharSet.Auto)]
  public static extern int RegOpenKeyEx(
    UIntPtr hKey,
    string subKey,
    int ulOptions,
    int samDesired,
    out UIntPtr hkResult);

In order to get a handle, I am using SafeHandle.DangerousHandle() which returns an IntPtr:

   /// <summary>
    /// Get a pointer to a registry key.
    /// </summary>
    /// <param name="registryKey">Registry key to obtain the pointer of.</param>
    /// <returns>Pointer to the given registry key.</returns>
    IntPtr _getRegistryKeyHandle(RegistryKey registryKey)
    {
        //Get the type of the RegistryKey
        Type registryKeyType = typeof(RegistryKey);

        //Get the FieldInfo of the 'hkey' member of RegistryKey
        System.Reflection.FieldInfo fieldInfo =
            registryKeyType.GetField("hkey", System.Reflection.BindingFlags.NonPublic | System.Reflection.BindingFlags.Instance);

        //Get the handle held by hkey
        SafeHandle handle = (SafeHandle)fieldInfo.GetValue(registryKey);

        //Get the unsafe handle
        IntPtr dangerousHandle = handle.DangerousGetHandle();
        return dangerousHandle;
    }

Answer 1

After taking a look at msdn i noticed that both, UIntPtr and IntPtr, have the void* pointer conversion.

IntPtr a = ....;
UIntPtr b = (UIntPtr)a.ToPointer();

At this point you need unsafe code. The only way to avoid this is using the unchecked keyword and convert by using non-pointer types ( used here too ).

The reason why there is no conversion between the two pointers might be that UIntPtr like IntPtr does not have a fixed size because they are platform specific( see ).