passing nullable type to a P/invoked function

WDT · 06-26-2009, 10:05 AM

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

Code:

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

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

valaris · 06-26-2009, 10:15 AM

SetupDiGetClassDevs

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

Code:

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

WDT · 06-27-2009, 05:57 AM

Quote:

Originally Posted by valaris

SetupDiGetClassDevs

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

Code:

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

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.

theoobe · 06-27-2009, 08:48 AM

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

Code:

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

Code:

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

06-26-2009, 10:05 AM	#1
WDT Tha 1 Sick RAT Join Date: Dec 2003 Posts: 267	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: [DllImport("setupapi.dll", CharSet = CharSet.Auto, SetLastError = true)] static extern IntPtr SetupDiGetClassDevs(ref Guid ClassGuid, int? enumerator, IntPtr hwndParent, uint Flags); to be passable so I can avoid have to overload the function. __________________ A hundred Elephants can knock down the walls of a fortress... One diseased rat can kill everyone inside
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06-26-2009, 10:15 AM	#2
valaris Registered User Join Date: Jun 2008 Location: RING 0 Posts: 468	SetupDiGetClassDevs From looking at that I'd use the signature below and pass IntPtr.Zero for NULL. Code: [DllImport("setupapi.dll", CharSet = CharSet.Auto)] static extern IntPtr SetupDiGetClassDevs( // 1st form using a ClassGUID ref Guid ClassGuid, IntPtr Enumerator, IntPtr hwndParent, int Flags );
valaris is offline

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