Fixes:

Attached is a patch to allow libpq to determine if a field is null.

This is needed because text fields will return a PQgetlength() of 0
whether it is '' or NULL.  There is even a comment in the source noting
the fact.

I have changed the value of the 'len' field for NULL result fields.  If
the field is null, the len is set to -1 (NULL_LEN).  I have changed
PQgetlength() to return a 0 length for both '' and NULL.  A new function
PQgetisnull() returns true or false for NULL.

The only risk is to applications that do not use the suggested
PQgetlength() call, but read the result 'len' field directly.

As this is not recommended, I think we are safe here.

A separate documentation patch will be sent.

Submitted by: Bruce Momjian <maillist@candle.pha.pa.us>

diff --git a/src/interfaces/libpq/fe-exec.c b/src/interfaces/libpq/fe-exec.c
index 3959c079031656d9b674ddaa8c34ce11b99b29f3..b81ae8535b18939b96b428372731c856f86b55b0 100644 (file)
--- a/src/interfaces/libpq/fe-exec.c
+++ b/src/interfaces/libpq/fe-exec.c
@@ -7,7 +7,7 @@
  *
  *
  * IDENTIFICATION
- *    $Header: /cvsroot/pgsql/src/interfaces/libpq/fe-exec.c,v 1.14 1996/08/10 00:22:48 scrappy Exp $
+ *    $Header: /cvsroot/pgsql/src/interfaces/libpq/fe-exec.c,v 1.15 1996/08/13 01:34:27 scrappy Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -156,11 +156,9 @@ getTuple(PGconn *conn, PGresult* result, int binary)
   for (i=0;i<nfields;i++) {
     if (!(bmap & 0200)) {
        /* if the field value is absent, make it '\0' */
-       /* XXX this makes it impossible to distinguish NULL 
-          attributes from "".  Is that OK?   */
        tup[i].value = (char*)malloc(1);
        tup[i].value[0] = '\0';
-       tup[i].len = 0;
+       tup[i].len = NULL_LEN;
     }
     else {
       /* get the value length (the first four bytes are for length) */
@@ -1469,6 +1467,35 @@ PQgetlength(PGresult *res, int tup_num, int field_num)
                "PQgetlength: ERROR! field %d(of %d) of tuple %d(of %d) is not available", 
                field_num, res->numAttributes - 1, tup_num, res->ntups);
     }
-       
-    return res->tuples[tup_num][field_num].len;
+
+    if (res->tuples[tup_num][field_num].len != NULL_LEN)
+       return res->tuples[tup_num][field_num].len;
+    else
+       return 0;
   }
+
+/* PQgetisnull:
+     returns the null status of a field value.
+*/
+int
+PQgetisnull(PGresult *res, int tup_num, int field_num)
+{
+    if (!res) {
+      fprintf(stderr, "PQgetisnull() -- pointer to PQresult is null");
+        return (int)NULL;
+    }
+
+    if (tup_num > (res->ntups - 1 )||
+       field_num > (res->numAttributes - 1))  {
+       fprintf(stderr,
+               "PQgetisnull: ERROR! field %d(of %d) of tuple %d(of %d) is not available", 
+               field_num, res->numAttributes - 1, tup_num, res->ntups);
+    }
+
+    if (res->tuples[tup_num][field_num].len == NULL_LEN)
+       return 1;
+    else
+       return 0;
+  }
+
+

diff --git a/src/interfaces/libpq/libpq-fe.h b/src/interfaces/libpq/libpq-fe.h
index 84de505337389adeaeccad4f7977419c228ef024..78bd330414c7d664c8034bd5d1232b3c2745c2ac 100644 (file)
--- a/src/interfaces/libpq/libpq-fe.h
+++ b/src/interfaces/libpq/libpq-fe.h
@@ -6,7 +6,7 @@
  *
  * Copyright (c) 1994, Regents of the University of California
  *
- * $Id: libpq-fe.h,v 1.6 1996/08/06 16:16:50 scrappy Exp $
+ * $Id: libpq-fe.h,v 1.7 1996/08/13 01:34:29 scrappy Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -83,6 +83,9 @@ typedef struct pgresAttDesc {
    For binary tuples, the first four bytes of the value is the size,
    and the bytes afterwards are the value.  The binary value is 
    not guaranteed to be null-terminated.  In fact, it can have embedded nulls*/
+
+#define NULL_LEN       (-1)    /* pg_result len for NULL value */
+
 typedef struct pgresAttValue {
   int len; /* length in bytes of the value */
   char *value; /* actual value */
@@ -178,6 +181,7 @@ extern char* PQcmdStatus(PGresult *res);
 extern const char* PQoidStatus(PGresult *res);
 extern char* PQgetvalue(PGresult *res, int tup_num, int field_num);
 extern int PQgetlength(PGresult *res, int tup_num, int field_num);
+extern int PQgetisnull(PGresult *res, int tup_num, int field_num);
 extern void PQclear(PGresult* res);
 /* PQdisplayTuples() is a better version of PQprintTuples() */
 extern void PQdisplayTuples(PGresult *res,