From: Mark Hills <Mark.Hills@framestore.com>
To: pgsql-docs@postgresql.org
Subject: [PATCH] libpq: Return of NULL from PQexec
Date: Mon, 31 Oct 2011 12:09:45 +0000 (GMT)
Message-ID: <alpine.LFD.2.01.1110311204150.4558@sys880.ldn.framestore.com> (raw)
I'm sending the patch below for inclusion.
Originally I ran this by pgsql-hackers, just to confirm the docs (and not
the code) were in need of the fix, which seems to be the case:
http://archives.postgresql.org/pgsql-hackers/2011-09/msg00614.php
Thanks
--
Mark
---------- Forwarded message ----------
Date: Mon, 12 Sep 2011 16:40:28 +0100 (BST)
From: Mark Hills <mark.hills@framestore.com>
To: pgsql-hackers@postgresql.org
Subject: libpq: Return of NULL from PQexec
The libpq documentation for PQexec states:
"If a null pointer is returned, it should be treated like a
PGRES_FATAL_ERROR result"
But this contradicts the example programs; eg. from Example Program 1:
/* Start a transaction block */
res = PQexec(conn, "BEGIN");
if (PQresultStatus(res) != PGRES_COMMAND_OK)
{
fprintf(stderr, "BEGIN command failed: %s", PQerrorMessage(conn));
PQclear(res);
exit_nicely(conn);
}
which does not check if (res != NULL).
The example is not buggy -- PQresultStatus, PQerrorMessage and,
importantly, PQclear deal with the NULL value; eg. src/libpq/fq-exec.c:
ExecStatusType
PQresultStatus(const PGresult *res)
{
if (!res)
return PGRES_FATAL_ERROR;
return res->resultStatus;
}
So I took the example to be correct, and attempted to fix the
documentation in the patch below. I hope this is useful.
In a straw-poll of code I could find using libpq, I found most follows the
example and is reliant on libpq for its NULL check.
The same also applies to PQconnect functions -- and PQstatus, PQfinish,
which I also tried to clarify in the documentation.
Thanks
--
Mark
inline patch 1: doc/src/sgml/libpq.sgml (+5/-3 lines) download inline-1.patchdiff --git a/doc/src/sgml/libpq.sgml b/doc/src/sgml/libpq.sgmlindex 163a893..57be7e1 100644--- a/doc/src/sgml/libpq.sgml+++ b/doc/src/sgml/libpq.sgml@@ -62,7 +62,7 @@
return a non-null object pointer, unless perhaps there is too
little memory even to allocate the <structname>PGconn</> object.
The <function>PQstatus</> function should be called to check
- whether a connection was successfully made before queries are sent+ the return value for a successful connection before queries are sent
via the connection object.
<warning>
@@ -1748,8 +1748,10 @@ PGresult *PQexec(PGconn *conn, const char *command);
Returns a <structname>PGresult</structname> pointer or possibly a null
pointer. A non-null pointer will generally be returned except in
out-of-memory conditions or serious errors such as inability to send
- the command to the server. If a null pointer is returned, it should- be treated like a <symbol>PGRES_FATAL_ERROR</symbol> result. Use+ the command to the server. The <function>PQresultStatus</> function+ should be called to check the return value for any errors (including+ the value of a null pointer, in which case it will return+ <symbol>PGRES_FATAL_ERROR</symbol>). Use
<function>PQerrorMessage</function> to get more information about such
errors.
</para>
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To: pgsql-docs@postgresql.org
Cc: Mark.Hills@framestore.com
Subject: Re: [PATCH] libpq: Return of NULL from PQexec
In-Reply-To: <alpine.LFD.2.01.1110311204150.4558@sys880.ldn.framestore.com>
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