C# and NULL pointers

Many DTWAIN functions that process strings allows the string parameter to be NULL.  For example, the DTWAIN_GetErrorString function has the option to set the string parameter to NULL if the caller only desires to have the length of the error string returned.

For C# applications, you must use the following for sending NULL pointers to DTWAIN:

For 32-bit applications:

System.IntPtr.Zero

For 64-bit applications:

System.LongPtr.Zero

For example, to call DTWAIN_GetErrorString with a NULL pointer (assume this is a 32-bit application).

namespace WindowsApplication

{

   using Dynarithmic;

   static void Main()

   {

            //...

            // get the length of the error message

            int eLength = TwainAPI.DTWAIN_GetErrorString( TwainAPI.DTWAIN_ERR_BAD_SOURCE, System.IntPtr.Zero, 0 );

            // size our string buffer appropriately and call again to get the string

            StringBuilder sText = new StringBuilder( eLength );

            TwainAPI.DTWAIN_GetErrorString( TwainAPI.DTWAIN_ERR_BAD_SOURCE, sText, eLength );

   }

}