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>Chapter 31. <SPAN
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><DIV
CLASS="SECT1"
><H1
CLASS="SECT1"
><A
NAME="LIBPQ-STATUS"
>31.2. Connection Status Functions</A
></H1
><P
>   These functions can be used to interrogate the status
   of an existing database connection object.
  </P
><DIV
CLASS="TIP"
><BLOCKQUOTE
CLASS="TIP"
><P
><B
>Tip: </B
>    
    
    <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
>.
    Reference to internal <TT
CLASS="STRUCTNAME"
>PGconn</TT
> fields using
    <TT
CLASS="FILENAME"
>libpq-int.h</TT
> is not recommended because they are subject to change
    in the future.
   </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
><A
NAME="LIBPQ-PQDB"
></A
><CODE
CLASS="FUNCTION"
>PQdb</CODE
>
      </DT
><DD
><P
>       Returns the database name of the connection.
</P><PRE
CLASS="SYNOPSIS"
>char *PQdb(const PGconn *conn);</PRE
><P>
      </P
></DD
><DT
><A
NAME="LIBPQ-PQUSER"
></A
><CODE
CLASS="FUNCTION"
>PQuser</CODE
>
      </DT
><DD
><P
>       Returns the user name of the connection.
</P><PRE
CLASS="SYNOPSIS"
>char *PQuser(const PGconn *conn);</PRE
><P>
      </P
></DD
><DT
><A
NAME="LIBPQ-PQPASS"
></A
><CODE
CLASS="FUNCTION"
>PQpass</CODE
>
      </DT
><DD
><P
>       Returns the password of the connection.
</P><PRE
CLASS="SYNOPSIS"
>char *PQpass(const PGconn *conn);</PRE
><P>
      </P
></DD
><DT
><A
NAME="LIBPQ-PQHOST"
></A
><CODE
CLASS="FUNCTION"
>PQhost</CODE
>
      </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
><A
NAME="LIBPQ-PQPORT"
></A
><CODE
CLASS="FUNCTION"
>PQport</CODE
>
      </DT
><DD
><P
>       Returns the port of the connection.

</P><PRE
CLASS="SYNOPSIS"
>char *PQport(const PGconn *conn);</PRE
><P>
      </P
></DD
><DT
><A
NAME="LIBPQ-PQTTY"
></A
><CODE
CLASS="FUNCTION"
>PQtty</CODE
>
      </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       (This is obsolete, since the server no longer pays attention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 backward compatibility.)

</P><PRE
CLASS="SYNOPSIS"
>char *PQtty(const PGconn *conn);</PRE
><P>
      </P
></DD
><DT
><A
NAME="LIBPQ-PQOPTIONS"
></A
><CODE
CLASS="FUNCTION"
>PQoptions</CODE
>
      </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
><A
NAME="LIBPQ-PQSTATUS"
></A
><CODE
CLASS="FUNCTION"
>PQstatus</CODE
>
      </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"
>PQconnectStartParams</CODE
>, <CODE
CLASS="FUNCTION"
>PQconnectStart</CODE
>
       and <CODE
CLASS="FUNCTION"
>PQconnectPoll</CODE
> with regards to other status codes that
       might be returned.
      </P
></DD
><DT
><A
NAME="LIBPQ-PQTRANSACTIONSTATUS"
></A
><CODE
CLASS="FUNCTION"
>PQtransactionStatus</CODE
>
      </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
><A
NAME="LIBPQ-PQPARAMETERSTATUS"
></A
><CODE
CLASS="FUNCTION"
>PQparameterStatus</CODE
>
      </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="VARNAME"
>server_version</TT
>,
       <TT
CLASS="VARNAME"
>server_encoding</TT
>,
       <TT
CLASS="VARNAME"
>client_encoding</TT
>,
       <TT
CLASS="VARNAME"
>application_name</TT
>,
       <TT
CLASS="VARNAME"
>is_superuser</TT
>,
       <TT
CLASS="VARNAME"
>session_authorization</TT
>,
       <TT
CLASS="VARNAME"
>DateStyle</TT
>,
       <TT
CLASS="VARNAME"
>IntervalStyle</TT
>,
       <TT
CLASS="VARNAME"
>TimeZone</TT
>,
       <TT
CLASS="VARNAME"
>integer_datetimes</TT
>, and
       <TT
CLASS="VARNAME"
>standard_conforming_strings</TT
>.
       (<TT
CLASS="VARNAME"
>server_encoding</TT
>, <TT
CLASS="VARNAME"
>TimeZone</TT
>, and
       <TT
CLASS="VARNAME"
>integer_datetimes</TT
> were not reported by releases before 8.0;
       <TT
CLASS="VARNAME"
>standard_conforming_strings</TT
> was not reported by releases
       before 8.1;
       <TT
CLASS="VARNAME"
>IntervalStyle</TT
> was not reported by releases before 8.4;
       <TT
CLASS="VARNAME"
>application_name</TT
> was not reported by releases before 9.0.)
       Note that
       <TT
CLASS="VARNAME"
>server_version</TT
>,
       <TT
CLASS="VARNAME"
>server_encoding</TT
> and
       <TT
CLASS="VARNAME"
>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="VARNAME"
>server_version</TT
> and <TT
CLASS="VARNAME"
>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="VARNAME"
>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="VARNAME"
>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
>       If no value for <TT
CLASS="VARNAME"
>standard_conforming_strings</TT
> is reported,
       applications can assume it is <TT
CLASS="LITERAL"
>off</TT
>, that is, backslashes
       are treated as escapes in string literals.  Also, the presence of
       this parameter can be taken as an indication that the escape string
       syntax (<TT
CLASS="LITERAL"
>E'...'</TT
>) is accepted.
      </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
><A
NAME="LIBPQ-PQPROTOCOLVERSION"
></A
><CODE
CLASS="FUNCTION"
>PQprotocolVersion</CODE
>
      </DT
><DD
><P
>       Interrogates the frontend/backend protocol being used.
</P><PRE
CLASS="SYNOPSIS"
>int PQprotocolVersion(const PGconn *conn);</PRE
><P>
       Applications might wish to use this function to determine whether certain
       features are supported.  Currently, the possible values are 2 (2.0
       protocol), 3 (3.0 protocol), or zero (connection bad).  The
       protocol version 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
><A
NAME="LIBPQ-PQSERVERVERSION"
></A
><CODE
CLASS="FUNCTION"
>PQserverVersion</CODE
>
      </DT
><DD
><P
>       Returns an integer representing the backend version.
</P><PRE
CLASS="SYNOPSIS"
>int PQserverVersion(const PGconn *conn);</PRE
><P>
       Applications might use this function 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 8.1.5
       will be returned as 80105, and version 8.2 will be returned as
       80200 (leading zeroes are not shown).  Zero is returned if the
       connection is bad.
      </P
></DD
><DT
><A
NAME="LIBPQ-PQERRORMESSAGE"
></A
><CODE
CLASS="FUNCTION"
>PQerrorMessage</CODE
>
      </DT
><DD
><P
>        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 can consist of multiple lines,
       and 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
><A
NAME="LIBPQ-PQSOCKET"
></A
><CODE
CLASS="FUNCTION"
>PQsocket</CODE
></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
><A
NAME="LIBPQ-PQBACKENDPID"
></A
><CODE
CLASS="FUNCTION"
>PQbackendPID</CODE
></DT
><DD
><P
>       Returns the process <ACRONYM
CLASS="ACRONYM"
>ID</ACRONYM
> (PID)
       of the backend 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
><A
NAME="LIBPQ-PQCONNECTIONNEEDSPASSWORD"
></A
><CODE
CLASS="FUNCTION"
>PQconnectionNeedsPassword</CODE
></DT
><DD
><P
>       Returns true (1) if the connection authentication method
       required a password, but none was available.
       Returns false (0) if not.

</P><PRE
CLASS="SYNOPSIS"
>int PQconnectionNeedsPassword(const PGconn *conn);</PRE
><P>
      </P
><P
>       This function can be applied after a failed connection attempt
       to decide whether to prompt the user for a password.
      </P
></DD
><DT
><A
NAME="LIBPQ-PQCONNECTIONUSEDPASSWORD"
></A
><CODE
CLASS="FUNCTION"
>PQconnectionUsedPassword</CODE
></DT
><DD
><P
>       Returns true (1) if the connection authentication method
       used a password. Returns false (0) if not.

</P><PRE
CLASS="SYNOPSIS"
>int PQconnectionUsedPassword(const PGconn *conn);</PRE
><P>
      </P
><P
>       This function can be applied after either a failed or successful
       connection attempt to detect whether the server demanded a password.
      </P
></DD
><DT
><A
NAME="LIBPQ-PQGETSSL"
></A
><CODE
CLASS="FUNCTION"
>PQgetssl</CODE
></DT
><DD
><P
>       
       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 so will also
       automatically include <TT
CLASS="FILENAME"
>ssl.h</TT
> from
       <SPAN
CLASS="PRODUCTNAME"
>OpenSSL</SPAN
>.
      </P
></DD
></DL
></DIV
><P>
  </P
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