passing nullable type to a P/invoked function

This is a discussion on passing nullable type to a P/invoked function within the C# Programming forums, part of the General Programming Boards category; Does anyone know of a way I can pass a nullable type to a p/invoked function? specifically I need parameter ...

  1. #1
    WDT
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    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

  2. #2
    Registered User valaris's Avatar
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    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
    );

  3. #3
    WDT
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    Quote Originally Posted by valaris View Post
    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.
    A hundred Elephants can knock down the walls of a fortress... One diseased rat can kill everyone inside

  4. #4
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    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, ...........

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