I've got some source code that includes vector and matrix classes (or
structures) that have addition and subtraction operators.  This source code
compiles on five different Unix platforms, but I'm getting a compiler error
on Vis C++.  The error is:

"binary operator + has too many parameters".

Here is the offending code fragment:

class ground_point_struct {
. . .
ground_point_struct     // return value
operator +(                   // addition operator
  ground_point_struct &gp1,    // ground point
  ground_point_struct &gp2 )   // ground point to subtract
{ .... }

Does anyone have any idea why Vis C++ wont compile this addition method?