Make length() disregard trailing spaces in char(n) values, per discussion

some time ago and recent patch from Gavin Sherry.  Update documentation
to point out that trailing spaces are insignificant in char(n).

doc/src/sgml/datatype.sgml

 <!--
-$PostgreSQL: pgsql/doc/src/sgml/datatype.sgml,v 1.140 2004/01/20 22:46:06 tgl Exp $
+$PostgreSQL: pgsql/doc/src/sgml/datatype.sgml,v 1.141 2004/02/01 06:27:48 tgl Exp $
 -->
 
  <chapter id="datatype">
@@ -901,6 +901,18 @@ CREATE TABLE <replaceable class="parameter">tablename</replaceable> (
     management systems have it as well.
    </para>
 
+   <para>
+    Values of type <type>character</type> are physically padded
+    with spaces to the specified width <replaceable>n</>, and are
+    stored and displayed that way.  However, the padding spaces are
+    treated as semantically insignificant.  Trailing spaces are
+    disregarded when comparing two values of type <type>character</type>,
+    and they will be removed when converting a <type>character</type> value
+    to one of the other string types.  Note that trailing spaces
+    <emphasis>are</> semantically significant in
+    <type>character varying</type> and <type>text</type> values.
+   </para>
+
    <para>
     The storage requirement for data of these types is 4 bytes plus the
     actual string, and in case of <type>character</type> plus the
@@ -922,7 +934,11 @@ CREATE TABLE <replaceable class="parameter">tablename</replaceable> (
     <para>
      There are no performance differences between these three types,
      apart from the increased storage size when using the blank-padded
-     type.
+     type.  While <type>character(<replaceable>n</>)</type> has performance
+     advantages in some other database systems, it has no such advantages in
+     <productname>PostgreSQL</productname>.  In most situations
+     <type>text</type> or <type>character varying</type> should be used
+     instead.
     </para>
    </tip>
 

src/backend/utils/adt/varchar.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/utils/adt/varchar.c,v 1.103 2003/11/29 19:51:59 pgsql Exp $
+ *	  $PostgreSQL: pgsql/src/backend/utils/adt/varchar.c,v 1.104 2004/02/01 06:27:48 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -510,14 +510,16 @@ Datum
 bpcharlen(PG_FUNCTION_ARGS)
 {
 	BpChar	   *arg = PG_GETARG_BPCHAR_P(0);
+	int			len;
 
-	/* optimization for single byte encoding */
-	if (pg_database_encoding_max_length() <= 1)
-		PG_RETURN_INT32(VARSIZE(arg) - VARHDRSZ);
+	/* get number of bytes, ignoring trailing spaces */
+	len = bcTruelen(arg);
+	
+	/* in multibyte encoding, convert to number of characters */
+	if (pg_database_encoding_max_length() != 1)
+		len = pg_mbstrlen_with_len(VARDATA(arg), len);
 
-	PG_RETURN_INT32(
-			  pg_mbstrlen_with_len(VARDATA(arg), VARSIZE(arg) - VARHDRSZ)
-		);
+	PG_RETURN_INT32(len);
 }
 
 Datum