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CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="LIBPQ-STATUS"
>27.2. Connection Status Functions</A
></H1
><P
> These functions may be used to interrogate the status
of an existing database connection object.
</P
><DIV
CLASS="TIP"
><BLOCKQUOTE
CLASS="TIP"
><P
><B
>Tip: </B
><A
NAME="AEN22900"
></A
>
<A
NAME="AEN22902"
></A
>
<SPAN
CLASS="APPLICATION"
>libpq</SPAN
> application programmers should be careful to
maintain the <TT
CLASS="STRUCTNAME"
>PGconn</TT
> abstraction. Use the accessor
functions described below to get
at the contents of <TT
CLASS="STRUCTNAME"
>PGconn</TT
>. Avoid directly referencing the fields of the
<TT
CLASS="STRUCTNAME"
>PGconn</TT
> structure because they are subject to change in the future.
(Beginning in <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> release 6.4, the
definition of the <TT
CLASS="TYPE"
>struct</TT
> behind <TT
CLASS="STRUCTNAME"
>PGconn</TT
> is not even provided in <TT
CLASS="FILENAME"
>libpq-fe.h</TT
>.
If you have old code that accesses <TT
CLASS="STRUCTNAME"
>PGconn</TT
> fields directly, you can keep using it
by including <TT
CLASS="FILENAME"
>libpq-int.h</TT
> too, but you are encouraged to fix the code
soon.)</P
></BLOCKQUOTE
></DIV
><P
>The following functions return parameter values established at connection.
These values are fixed for the life of the <TT
CLASS="STRUCTNAME"
>PGconn</TT
> object.
<P
></P
></P><DIV
CLASS="VARIABLELIST"
><DL
><DT
><CODE
CLASS="FUNCTION"
>PQdb</CODE
><A
NAME="AEN22920"
></A
></DT
><DD
><P
> Returns the database name of the connection.
</P><PRE
CLASS="SYNOPSIS"
>char *PQdb(const PGconn *conn);</PRE
><P></P
></DD
><DT
><CODE
CLASS="FUNCTION"
>PQuser</CODE
><A
NAME="AEN22928"
></A
></DT
><DD
><P
> Returns the user name of the connection.
</P><PRE
CLASS="SYNOPSIS"
>char *PQuser(const PGconn *conn);</PRE
><P></P
></DD
><DT
><CODE
CLASS="FUNCTION"
>PQpass</CODE
><A
NAME="AEN22936"
></A
></DT
><DD
><P
> Returns the password of the connection.
</P><PRE
CLASS="SYNOPSIS"
>char *PQpass(const PGconn *conn);</PRE
><P></P
></DD
><DT
><CODE
CLASS="FUNCTION"
>PQhost</CODE
><A
NAME="AEN22944"
></A
></DT
><DD
><P
> Returns the server host name of the connection.
</P><PRE
CLASS="SYNOPSIS"
>char *PQhost(const PGconn *conn);</PRE
><P></P
></DD
><DT
><CODE
CLASS="FUNCTION"
>PQport</CODE
><A
NAME="AEN22952"
></A
></DT
><DD
><P
> Returns the port of the connection.
</P><PRE
CLASS="SYNOPSIS"
>char *PQport(const PGconn *conn);</PRE
><P></P
></DD
><DT
><CODE
CLASS="FUNCTION"
>PQtty</CODE
><A
NAME="AEN22960"
></A
></DT
><DD
><P
> Returns the debug <ACRONYM
CLASS="ACRONYM"
>TTY</ACRONYM
> of the connection.
(This is obsolete, since the server no longer pays attention
to the <ACRONYM
CLASS="ACRONYM"
>TTY</ACRONYM
> setting, but the function remains
for backwards compatibility.)
</P><PRE
CLASS="SYNOPSIS"
>char *PQtty(const PGconn *conn);</PRE
><P></P
></DD
><DT
><CODE
CLASS="FUNCTION"
>PQoptions</CODE
><A
NAME="AEN22970"
></A
></DT
><DD
><P
> Returns the command-line options passed in the connection request.
</P><PRE
CLASS="SYNOPSIS"
>char *PQoptions(const PGconn *conn);</PRE
><P></P
></DD
></DL
></DIV
><P></P
><P
>The following functions return status data that can change as operations
are executed on the <TT
CLASS="STRUCTNAME"
>PGconn</TT
> object.
<P
></P
></P><DIV
CLASS="VARIABLELIST"
><DL
><DT
><CODE
CLASS="FUNCTION"
>PQstatus</CODE
><A
NAME="AEN22981"
></A
></DT
><DD
><P
> Returns the status of the connection.
</P><PRE
CLASS="SYNOPSIS"
>ConnStatusType PQstatus(const PGconn *conn);</PRE
><P></P
><P
> The status can be one of a number of values.
However, only two of these are
seen outside of an asynchronous connection procedure:
<TT
CLASS="LITERAL"
>CONNECTION_OK</TT
> and
<TT
CLASS="LITERAL"
>CONNECTION_BAD</TT
>. A good
connection to the database has the status <TT
CLASS="LITERAL"
>CONNECTION_OK</TT
>.
A failed connection
attempt is signaled by status
<TT
CLASS="LITERAL"
>CONNECTION_BAD</TT
>.
Ordinarily, an OK status will remain so until
<CODE
CLASS="FUNCTION"
>PQfinish</CODE
>, but a
communications failure might result in the status changing to
<TT
CLASS="LITERAL"
>CONNECTION_BAD</TT
> prematurely.
In that case the application
could try to recover by calling <CODE
CLASS="FUNCTION"
>PQreset</CODE
>.
</P
><P
> See the entry for <CODE
CLASS="FUNCTION"
>PQconnectStart</CODE
> and <CODE
CLASS="FUNCTION"
>PQconnectPoll</CODE
> with regards
to other status codes
that might be seen.
</P
></DD
><DT
><CODE
CLASS="FUNCTION"
>PQtransactionStatus</CODE
><A
NAME="AEN23000"
></A
></DT
><DD
><P
> Returns the current in-transaction status of the server.
</P><PRE
CLASS="SYNOPSIS"
>PGTransactionStatusType PQtransactionStatus(const PGconn *conn);</PRE
><P>
The status can be <TT
CLASS="LITERAL"
>PQTRANS_IDLE</TT
> (currently idle),
<TT
CLASS="LITERAL"
>PQTRANS_ACTIVE</TT
> (a command is in progress),
<TT
CLASS="LITERAL"
>PQTRANS_INTRANS</TT
> (idle, in a valid transaction block),
or <TT
CLASS="LITERAL"
>PQTRANS_INERROR</TT
> (idle, in a failed transaction block).
<TT
CLASS="LITERAL"
>PQTRANS_UNKNOWN</TT
> is reported if the connection is bad.
<TT
CLASS="LITERAL"
>PQTRANS_ACTIVE</TT
> is reported only when a query
has been sent to the server and not yet completed.</P
><DIV
CLASS="CAUTION"
><P
></P
><TABLE
CLASS="CAUTION"
BORDER="1"
WIDTH="90%"
><TR
><TD
ALIGN="CENTER"
><B
>Caution</B
></TD
></TR
><TR
><TD
ALIGN="LEFT"
><P
><CODE
CLASS="FUNCTION"
>PQtransactionStatus</CODE
> will give incorrect results when using
a <SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> 7.3 server that has the parameter <TT
CLASS="LITERAL"
>autocommit</TT
>
set to off. The server-side autocommit feature has been
deprecated and does not exist in later server versions.</P
></TD
></TR
></TABLE
></DIV
></DD
><DT
><CODE
CLASS="FUNCTION"
>PQparameterStatus</CODE
><A
NAME="AEN23019"
></A
></DT
><DD
><P
> Looks up a current parameter setting of the server.
</P><PRE
CLASS="SYNOPSIS"
>const char *PQparameterStatus(const PGconn *conn, const char *paramName);</PRE
><P>
Certain parameter values are reported by the server automatically at
connection startup or whenever their values change.
<CODE
CLASS="FUNCTION"
>PQparameterStatus</CODE
> can be used to interrogate these settings.
It returns the current value of a parameter if known, or <TT
CLASS="SYMBOL"
>NULL</TT
>
if the parameter is not known.</P
><P
>Parameters reported as of the current release include
<TT
CLASS="LITERAL"
>server_version</TT
>,
<TT
CLASS="LITERAL"
>server_encoding</TT
>,
<TT
CLASS="LITERAL"
>client_encoding</TT
>,
<TT
CLASS="LITERAL"
>is_superuser</TT
>,
<TT
CLASS="LITERAL"
>session_authorization</TT
>,
<TT
CLASS="LITERAL"
>DateStyle</TT
>,
<TT
CLASS="LITERAL"
>TimeZone</TT
>, and
<TT
CLASS="LITERAL"
>integer_datetimes</TT
>.
(<TT
CLASS="LITERAL"
>server_encoding</TT
>, <TT
CLASS="LITERAL"
>TimeZone</TT
>, and
<TT
CLASS="LITERAL"
>integer_datetimes</TT
> were not reported by releases before 8.0.)
Note that
<TT
CLASS="LITERAL"
>server_version</TT
>,
<TT
CLASS="LITERAL"
>server_encoding</TT
> and
<TT
CLASS="LITERAL"
>integer_datetimes</TT
>
cannot change after startup.</P
><P
>Pre-3.0-protocol servers do not report parameter settings, but
<SPAN
CLASS="APPLICATION"
>libpq</SPAN
> includes logic to obtain values for
<TT
CLASS="LITERAL"
>server_version</TT
> and <TT
CLASS="LITERAL"
>client_encoding</TT
> anyway.
Applications are encouraged to use <CODE
CLASS="FUNCTION"
>PQparameterStatus</CODE
>
rather than <I
CLASS="FOREIGNPHRASE"
>ad hoc</I
> code to determine these values.
(Beware however
that on a pre-3.0 connection, changing <TT
CLASS="LITERAL"
>client_encoding</TT
> via
<TT
CLASS="COMMAND"
>SET</TT
> after connection startup will not be reflected by
<CODE
CLASS="FUNCTION"
>PQparameterStatus</CODE
>.) For <TT
CLASS="LITERAL"
>server_version</TT
>,
see also <CODE
CLASS="FUNCTION"
>PQserverVersion</CODE
>, which returns the information
in a numeric form that is much easier to compare against.</P
><P
>Although the returned pointer is declared <TT
CLASS="LITERAL"
>const</TT
>, it in fact
points to mutable storage associated with the <TT
CLASS="LITERAL"
>PGconn</TT
> structure.
It is unwise to assume the pointer will remain valid across queries.</P
></DD
><DT
><CODE
CLASS="FUNCTION"
>PQprotocolVersion</CODE
><A
NAME="AEN23058"
></A
></DT
><DD
><P
> Interrogates the frontend/backend protocol being used.
</P><PRE
CLASS="SYNOPSIS"
>int PQprotocolVersion(const PGconn *conn);</PRE
><P>
Applications may wish to use this to determine whether certain features
are supported.
Currently, the possible values are 2 (2.0 protocol), 3 (3.0 protocol),
or zero (connection bad). This will not change after connection
startup is complete, but it could theoretically change during a connection
reset. The 3.0 protocol will normally be used when communicating with
<SPAN
CLASS="PRODUCTNAME"
>PostgreSQL</SPAN
> 7.4 or later servers; pre-7.4 servers support
only protocol 2.0. (Protocol 1.0 is obsolete and not supported by <SPAN
CLASS="APPLICATION"
>libpq</SPAN
>.)</P
></DD
><DT
><CODE
CLASS="FUNCTION"
>PQserverVersion</CODE
><A
NAME="AEN23068"
></A
></DT
><DD
><P
> Returns an integer representing the backend version.
</P><PRE
CLASS="SYNOPSIS"
>int PQserverVersion(const PGconn *conn);</PRE
><P>
Applications may use this to determine the version of the database server they
are connected to. The number is formed by converting the major, minor, and
revision numbers into two-decimal-digit numbers and appending them
together. For example, version 7.4.2 will be returned as 70402, and version
8.1 will be returned as 80100 (leading zeroes are not shown). Zero is
returned if the connection is bad.</P
></DD
><DT
><CODE
CLASS="FUNCTION"
>PQerrorMessage</CODE
><A
NAME="AEN23076"
></A
></DT
><DD
><P
> <A
NAME="AEN23080"
></A
>
Returns the error message most recently generated by
an operation on the connection.
</P><PRE
CLASS="SYNOPSIS"
>char *PQerrorMessage(const PGconn *conn);</PRE
><P>
</P
><P
> Nearly all <SPAN
CLASS="APPLICATION"
>libpq</SPAN
> functions will set a message for
<CODE
CLASS="FUNCTION"
>PQerrorMessage</CODE
> if they fail.
Note that by <SPAN
CLASS="APPLICATION"
>libpq</SPAN
> convention, a nonempty
<CODE
CLASS="FUNCTION"
>PQerrorMessage</CODE
> result will
include a trailing newline. The caller should not free the result
directly. It will be freed when the associated <TT
CLASS="STRUCTNAME"
>PGconn</TT
>
handle is passed to <CODE
CLASS="FUNCTION"
>PQfinish</CODE
>. The result string
should not be expected to remain the same across operations on the
<TT
CLASS="LITERAL"
>PGconn</TT
> structure.
</P
></DD
><DT
><CODE
CLASS="FUNCTION"
>PQsocket</CODE
><A
NAME="AEN23094"
></A
></DT
><DD
><P
> Obtains the file descriptor number of the connection socket to
the server. A valid descriptor will be greater than or equal
to 0; a result of -1 indicates that no server connection is
currently open. (This will not change during normal operation,
but could change during connection setup or reset.)
</P><PRE
CLASS="SYNOPSIS"
>int PQsocket(const PGconn *conn);</PRE
><P>
</P
></DD
><DT
><CODE
CLASS="FUNCTION"
>PQbackendPID</CODE
><A
NAME="AEN23102"
></A
></DT
><DD
><P
> Returns the process <ACRONYM
CLASS="ACRONYM"
>ID</ACRONYM
>
(PID)<A
NAME="AEN23107"
></A
> of the backend server
process handling this connection.
</P><PRE
CLASS="SYNOPSIS"
>int PQbackendPID(const PGconn *conn);</PRE
><P></P
><P
> The backend <ACRONYM
CLASS="ACRONYM"
>PID</ACRONYM
> is useful for debugging
purposes and for comparison to <TT
CLASS="COMMAND"
>NOTIFY</TT
>
messages (which include the <ACRONYM
CLASS="ACRONYM"
>PID</ACRONYM
> of the
notifying backend process). Note that the
<ACRONYM
CLASS="ACRONYM"
>PID</ACRONYM
> belongs to a process executing on the
database server host, not the local host!
</P
></DD
><DT
><CODE
CLASS="FUNCTION"
>PQgetssl</CODE
><A
NAME="AEN23120"
></A
></DT
><DD
><P
> <A
NAME="AEN23124"
></A
>
Returns the SSL structure used in the connection, or null
if SSL is not in use.
</P><PRE
CLASS="SYNOPSIS"
>SSL *PQgetssl(const PGconn *conn);</PRE
><P></P
><P
> This structure can be used to verify encryption levels, check
server certificates, and more. Refer to the <SPAN
CLASS="PRODUCTNAME"
>OpenSSL</SPAN
> documentation
for information about this structure.
</P
><P
> You must define <TT
CLASS="SYMBOL"
>USE_SSL</TT
> in order to get the
correct prototype for this function. Doing this will also
automatically include <TT
CLASS="FILENAME"
>ssl.h</TT
> from <SPAN
CLASS="PRODUCTNAME"
>OpenSSL</SPAN
>.
</P
></DD
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