Add comments describing interface to heap_getattr().

src/backend/access/common/heaptuple.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *    $Header: /cvsroot/pgsql/src/backend/access/common/heaptuple.c,v 1.17 1996/12/04 03:05:55 bryanh Exp $
+ *    $Header: /cvsroot/pgsql/src/backend/access/common/heaptuple.c,v 1.18 1996/12/09 01:22:17 bryanh Exp $
  *
  * NOTES
  *    The old interface functions have been converted to macros
@@ -660,9 +660,18 @@ fastgetattr(HeapTuple tup,
 /* ----------------
  *      heap_getattr
  *
- *	returns an attribute from a heap tuple.  uses 
- * ----------------
- */
+ *      Find a particular field in a row represented as a heap tuple.
+ *      We return a pointer into that heap tuple, which points to the
+ *      first byte of the value of the field in question.
+ *
+ *      If the field in question has a NULL value, we return a null
+ *      pointer and return <*isnull> == true.  Otherwise, we return
+ *      <*isnull> == false.
+ *
+ *      <tup> is the pointer to the heap tuple.  <attnum> is the attribute
+ *      number of the column (field) caller wants.  <tupleDesc> is a 
+ *      pointer to the structure describing the row and all its fields.
+ * ---------------- */
 char *
 heap_getattr(HeapTuple tup,
              Buffer b,