passing nullable type to a P/invoked function

Does anyone know of a way I can pass a nullable type to a p/invoked function? specifically I need parameter 1 of:

Code:

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[DllImport("setupapi.dll", CharSet = CharSet.Auto, SetLastError = true)]
    static extern IntPtr SetupDiGetClassDevs(ref Guid ClassGuid, int? enumerator, IntPtr hwndParent, uint Flags);

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to be passable so I can avoid have to overload the function.

SetupDiGetClassDevs

From looking at that I'd use the signature below and pass IntPtr.Zero for NULL.

Code:

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[DllImport("setupapi.dll", CharSet = CharSet.Auto)]
static extern IntPtr SetupDiGetClassDevs(          // 1st form using a ClassGUID
  ref Guid ClassGuid,
  IntPtr Enumerator,
  IntPtr hwndParent,
  int Flags
);

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Quote:

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Originally Posted by valaris

SetupDiGetClassDevs

From looking at that I'd use the signature below and pass IntPtr.Zero for NULL.

Code:

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[DllImport("setupapi.dll", CharSet = CharSet.Auto)]
static extern IntPtr SetupDiGetClassDevs(          // 1st form using a ClassGUID
  ref Guid ClassGuid,
  IntPtr Enumerator,
  IntPtr hwndParent,
  int Flags
);

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I meant parameter 1 of the function. not the enumerator the ref Guid ClassGuid variable. Also I should say I changed the enumerator to string type variable. The original posting of the function was a typo.

A Guid can't be null, but you can also use this second signature:

Code:

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[DllImport("setupapi.dll", CharSet = CharSet.Auto)]
static extern IntPtr SetupDiGetClassDevs(
  IntPtr ClassGuid,
  string Enumerator,
  IntPtr hwndParent,
  int Flags
);

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Code:

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SetupDiGetClassDevs(IntPtr.Zero, ...........

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