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Re: Problem calling function in DLL via NETLink: NET::netexcptn: A .NET exception occurred

• To: mathgroup at smc.vnet.net
• Subject: [mg66341] Re: [mg66319] Problem calling function in DLL via NETLink: NET::netexcptn: A .NET exception occurred
• From: Todd Gayley <tgayley at wolfram.com>
• Date: Wed, 10 May 2006 06:33:43 -0400 (EDT)
• Sender: owner-wri-mathgroup at wolfram.com

At 01:35 AM 5/9/2006, Heiko Damerau wrote:
>Hello,
>
>      I am trying to call a function in an ordinary C++ DLL (should be
>well tested, not my code). The DLL function I am calling is declared as
>
>      short SyncRPC FAR PASCAL SyncRPC(const char *locName, const char
>*locProperty, const char *locCycle, short ArraySize, void *Data, long
>DataSize, short DataFormat, short DataType)
>
>      As I do not need the full flexibility when called from Mathematica,
>it is defined as
>
>      DLLFunctionSyncRPC = DefineDLLFunction["SyncRPC", "rpcapi32.dll",
>"short", {"char*", "char*", "char*", "short", "byte[]", "byte", "short",
>"short"}];
>
>and finally called by
>
>      DLLFunctionSyncRPC[elementName, property, plsLine, optArraySize,
>netManagedDataArray, 0, 1, 0];
>
>where elementName, property, plsLine are Mathematica strings,
>optArraySize is an ordinary mathematica number (integer) and
>netManagedDataArray is a .NET object declared as
>
>      NETNew["System.Byte[]", 17optArraySize + 1];
>
>to get the pointer to the result. Everything works fine but sometimes I
>get strange error messages:
>
>NET::netexcptn: A .NET exception occurred:
>System.NullReferenceException: Object reference not set to an instance
>of an object. at
>Wolfram.NETLink.DynamicDLLNamespace.DLLWrapper612.SyncRPC(String ,
>String , String , Int16 , Byte[] , Byte , Int16 , Int16 )
>
>      and my notebook is not executed as it should. Changing nothing and
>just running the Mathematica notebook a second time and the error
>disappears most of the time. The error appears especially, when I call
>the DLL function extremely often; but also with a fresh kernel the error
>normally comes after some 25 calls of the function in the DLL.
>
>      It would be great if anyone could give me a hint what is wrong with
>my function calls, because most of the time everything works correctly.


Heiko,

One problem is that the "byte" type (DataSize) in your DefineDLLFunction 
should be "long."


Todd Gayley
Wolfram Research