error-c-.md

The following function divides two integers. To prevent division by zero, it tests the second parameter and fails if it is zero:

class Div2ints : public ScalarFunction
{
public:
  virtual void processBlock(ServerInterface &srvInterface,
                            BlockReader &arg_reader,
                            BlockWriter &res_writer)
  {
    // While we have inputs to process
    do
      {
        const vint a = arg_reader.getIntRef(0);
        const vint b = arg_reader.getIntRef(1);
        if (b == 0)
          {
            vt_report_error(1,"Attempted divide by zero");
          }
        res_writer.setInt(a/b);
        res_writer.next();
      }
    while (arg_reader.next());
  }
};

Loading and invoking the function demonstrates how the error appears to the user. Fenced and unfenced modes use different error numbers.

=> CREATE LIBRARY Div2IntsLib AS '/home/dbadmin/Div2ints.so';
CREATE LIBRARY
=> CREATE FUNCTION div2ints AS LANGUAGE 'C++' NAME 'Div2intsInfo' LIBRARY Div2IntsLib;
CREATE FUNCTION
=> SELECT div2ints(25, 5);
 div2ints
----------
        5
(1 row)
=> SELECT * FROM MyTable;
 a  | b
----+---
 12 | 6
  7 | 0
 12 | 2
 18 | 9
(4 rows)
=> SELECT * FROM MyTable WHERE div2ints(a, b) > 2;
ERROR 3399:  Error in calling processBlock() for User Defined Scalar Function
div2ints at Div2ints.cpp:21, error code: 1, message: Attempted divide by zero