SPI_getvalue — return the string value of the specified column
char * SPI_getvalue(HeapTuplerow, TupleDescrowdesc, intcolnumber)
   SPI_getvalue returns the string representation
   of the value of the specified column.
  
   The result is returned in memory allocated using
   palloc.  (You can use
   pfree to release the memory when you don't
   need it anymore.)
  
HeapTuple rowinput row to be examined
TupleDesc rowdescinput row description
int colnumbercolumn number (count starts at 1)
   Column value, or NULL if the column is null,
   colnumber is out of range
   (SPI_result is set to
   SPI_ERROR_NOATTRIBUTE), or no output function is
   available (SPI_result is set to
   SPI_ERROR_NOOUTFUNC).