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.NET Forum / .NET Framework / .NET SDK / September 2003DllImportAttribute CallingConvention
I am calling an unmanaged DLL like follows in a Class wrapper. namespace blah { [DllImport("DLLName.DLL", EntryPoint="BlahEntryPoint", CallingConvention=CallingConvention.ThisCall] public static extern void blahFn(out long blah, out long blah2); class sealed ClassBlah { private ClassBlah() { } } } Why have I to call this with the CallingConvention of ThisCall, its just normal "C" functions in a DLL. Why wont StdCall work? What happens with other calling conventions is that the out parameters are NOT set, yet with ThisCall, they are set ok, or appear to be. I find it odd. Thanks Mr. Tickle, What is the declaration of the original function? If it takes a pointer, then you should be using "ref" for the parameters, and not out. Also, does the function take a 64-bit integer? Long in C is a 32-bit integer, where in .NET it is a 64-bit integer. The STDCALL mechanism should work if you are using it. Hope this helps.  Signature- Nicholas Paldino [.NET/C# MVP] - nicholas.paldino@exisconsulting.com > I am calling an unmanaged DLL like follows in a Class wrapper. > [quoted text clipped - 20 lines] > > Thanks Nop, I tried ref and it doesnt help, the only way i can get it to return values is with thiscall. > Mr. Tickle, > [quoted text clipped - 36 lines] > > > > Thanks So i should use Int32 for the parameters instead of long? > Mr. Tickle, > [quoted text clipped - 36 lines] > > > > Thanks I also have a problem with "ref" paramaters, it says they need to be assigned to before used Yet i have them used as "ref" in dll extern calls and checked for non NULL after yet it complains for non assignment so i use a local copy. Isnt it smart enough to detect that its being assinged in an extern dll call as declared in DllImport? > Mr. Tickle, > [quoted text clipped - 36 lines] > > > > Thanks i mean "out" oops. ref in the same dll wrapper still gets the output but only with thiscall convention. > I also have a problem with "ref" paramaters, it says they need to be > assigned to before used [quoted text clipped - 47 lines] > > > > > > Thanks If you could post the original function declaration, it would help tremendously. Signature- Nicholas Paldino [.NET/C# MVP] - nicholas.paldino@exisconsulting.com > i mean "out" oops. > [quoted text clipped - 56 lines] > > > > > > > > Thanks It would but I dont have it, its in a dll i have to call into. Not mine. > If you could post the original function declaration, it would help > tremendously. [quoted text clipped - 66 lines] > > > > > > > > > > Thanks typedef SOME_ID long SOME_ID someFn(SOME_ID* someIDhere, SOME_ID* someIDhere2, SOME_ID* someIDhere3); something like that. > If you could post the original function declaration, it would help > tremendously. [quoted text clipped - 66 lines] > > > > > > > > > > Thanks Mr.Tickle, In this case, you definitely want to use the int type, and pass it by reference. Your declaration should look like this: [DllImport("somedll.dll")] public static extern int someFn(ref int someIDhere, ref int someIDhere2, ref int someIDhere3); Signature- Nicholas Paldino [.NET/C# MVP] - nicholas.paldino@exisconsulting.com > typedef SOME_ID long > [quoted text clipped - 77 lines] > > > > > > > > > > > > Thanks But I still dont understand why Thiscall works and the others dont. > Mr.Tickle, > [quoted text clipped - 98 lines] > > > > > > > > > > > > > > Thanks Because in you definition you only pass two arguments, while you need tree (an int, and to poiters). It works while using the thiscall calling convention, because the interop layer passes as first argument an int for the this pointer (three int's are reserved on the stack). Willy. > But I still dont understand why Thiscall works and the others dont. > [quoted text clipped - 106 lines] > > > > > > > > > > > > > > > > Thanks Well its suppost to match up, its just something i typed in a hurry but it is the same number of arguments in the definition and call. on teh real code. the dll definition would be typedef SOMEVAL long typedef SOME_ID long SOME_ID someFn(SOMEVAL someVal, SOME_ID* someIDhere, SOME_ID* someIDhere2, SOME_ID* someIDhere3); so im calling with for example out of my memory DllImport("somedll.dll", EntryPoint="blahFn", CallingConvention=CallingConvention.ThisCall)] public static extern int someFn(long someVal, ref someIDhere, ref long someIDhere2, ref long someIDhere3); // i know this should be int instead of long but curious why the long works with thiscall and not the others or just not work at all. long someVal; long ID someID, anotherID, yetAnohterID, andAnotherID; someID = blahFn(someVal, ref anotherID, ref yetAnotherID, ref andAnotherID); Only thiscall works, others dont, so if i understand it right I change the definition from long to int for 32bit instead of the 64bit on the .net side, and then i can use stdcall as normal. > Because in you definition you only pass two arguments, while you need tree (an int, and to poiters). > It works while using the thiscall calling convention, because the interop layer passes as first argument an int for the this pointer [quoted text clipped - 112 lines] > > > > > > > > > > > > > > > > > > Thanks Free MagazinesGet these publications absolutely FREE for up to 12 months. 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