Make text <=> char conversion functions convert zero character to and

from an empty text string.  This makes them consistent with the de facto
behavior of type char's I/O conversion functions, and avoids generating
text values with embedded nulls, which confuse many text operators.

diff --git a/src/backend/utils/adt/char.c b/src/backend/utils/adt/char.c
index 3237566fc5f4d1be2c80bebb875c2ee77ad3f951..dc6bd5e97655eb16e50916291d6262e5a2f141f1 100644 (file)
--- a/src/backend/utils/adt/char.c
+++ b/src/backend/utils/adt/char.c
@@ -9,7 +9,7 @@
  *
  *
  * IDENTIFICATION
- *   $Header: /cvsroot/pgsql/src/backend/utils/adt/char.c,v 1.30 2001/01/24 19:43:13 momjian Exp $
+ *   $Header: /cvsroot/pgsql/src/backend/utils/adt/char.c,v 1.31 2001/05/28 21:58:32 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -23,6 +23,8 @@
 
 /*
  *     charin          - converts "x" to 'x'
+ *
+ * Note that an empty input string will implicitly be converted to \0.
  */
 Datum
 charin(PG_FUNCTION_ARGS)
@@ -34,6 +36,10 @@ charin(PG_FUNCTION_ARGS)
 
 /*
  *     charout         - converts 'x' to "x"
+ *
+ * Note that if the char value is \0, the resulting string will appear
+ * to be empty (null-terminated after zero characters).  So this is the
+ * inverse of the charin() function for such data.
  */
 Datum
 charout(PG_FUNCTION_ARGS)
@@ -147,13 +153,24 @@ chardiv(PG_FUNCTION_ARGS)
    PG_RETURN_CHAR((int8) arg1 / (int8) arg2);
 }
 
+
 Datum
 text_char(PG_FUNCTION_ARGS)
 {
    text       *arg1 = PG_GETARG_TEXT_P(0);
+   char        result;
+
+   /*
+    * An empty input string is converted to \0 (for consistency with charin).
+    * If the input is longer than one character, the excess data is silently
+    * discarded.
+    */
+   if (VARSIZE(arg1) > VARHDRSZ)
+       result = *(VARDATA(arg1));
+   else
+       result = '\0';
 
-   /* XXX what if arg1 has length zero? */
-   PG_RETURN_CHAR(*(VARDATA(arg1)));
+   PG_RETURN_CHAR(result);
 }
 
 Datum
@@ -162,8 +179,19 @@ char_text(PG_FUNCTION_ARGS)
    char        arg1 = PG_GETARG_CHAR(0);
    text       *result = palloc(VARHDRSZ + 1);
 
-   VARATT_SIZEP(result) = VARHDRSZ + 1;
-   *(VARDATA(result)) = arg1;
+   /*
+    * Convert \0 to an empty string, for consistency with charout (and
+    * because the text stuff doesn't like embedded nulls all that well).
+    */
+   if (arg1 != '\0')
+   {
+       VARATT_SIZEP(result) = VARHDRSZ + 1;
+       *(VARDATA(result)) = arg1;
+   }
+   else
+   {
+       VARATT_SIZEP(result) = VARHDRSZ;
+   }
 
    PG_RETURN_TEXT_P(result);
 }