Calling C DLL from C#

Question

I am trying to call a C DLL from C#, but I\'m not having any joy. The documentation for the DLL provides an example function delaration for VB that looks like;

Answer 1

You may want to define your c# signatures using marshalling attributes for your string parameters.

[DllImport(@"c:\GDAit.dll")]
public static extern long TransGeogPt([MarshalAs(UnmanagedType.LPStr)] string sGridFile, long lDirection, double dLat, double dLong, ref double pdLatNew, ref double pdLongNew, ref double pdLatAcc, ref double pdLongAcc);

[DllImport(@"c:\GDAit.dll")]
public static extern long TransProjPt([MarshalAs(UnmanagedType.LPStr)] string sGridFile, long lDirection, double dLat, double dLong, long lZone, ref double pdLatNew, ref double pdLongNew, ref double pdLatAcc, ref double pdLongAcc);

I'll also piggy-back on Mark Sowul's answer and say try calling with StdCall instead of Cdecl.

Also, as a precaution, I'd probably double-check to make sure that the compiler is set to compile x86 code, in case its compiling for 64-bit.