PInvoke int32*

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Joe Franklin - 16 Nov 2004 19:33 GMT

If I have this method defined in a header file for a 3rd party DLL:

AT_RESULT_CODE ATGetVersion (
int32* piSensorVersion,
int32* piLibMajorVersion,
int32* piLibMinorVersion,
int32* piLibBuildVersion,
int32* piVersionCRC)

and I've defined it like this in my managed code:

[DllImport("atsc63.dll",CharSet=CharSet.Auto)]
public static extern int ATGetVersion (
ref Int32 sensorVer,
ref Int32 major,
ref Int32 minor,
ref Int32 build,
ref Int32 crc );

Is my definition correct? How do I pass null as the first param,
since I can't assign null to an Int32???

Joe

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Mattias Sj?gren - 16 Nov 2004 20:08 GMT

>Is my definition correct?

Yes it looks good.

>How do I pass null as the first param,
>since I can't assign null to an Int32???

If you want to pass in null you can change the parameter type to
IntPtr and pass in IntPtr.Zero.

Mattias

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Mattias Sjögren [MVP] mattias @ mvps.org
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Heath Stewart [MSFT] - 21 Nov 2004 09:01 GMT

If you declare the parameters as IntPtr, however, do not use ref IntPtr.
IntPtr is already a pointer to an int.

Alternatively, you could declare the parameters as objects (not ref
object, since object is already a reference type) and pass Missing.Value.

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Heath Stewart
Software Design Engineer
Developer Division Sustained Engineering
Microsoft Corporation

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Mattias Sj?gren - 26 Nov 2004 21:56 GMT

>Alternatively, you could declare the parameters as objects (not ref
>object, since object is already a reference type) and pass Missing.Value.

I don't think that works for PInvoke. Object parameters gets marshaled
as VARIANTs, which is very different from an int*. You could apply
MarshalAs(UnmanagedType.AsAny), but even then the runtime doesn't
handle Missing.Value as the argument.

Mattias

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Mattias Sjögren [MVP] mattias @ mvps.org
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PInvoke int32*

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