<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <HTML ><HEAD ><TITLE >libpq - C Library</TITLE ><META NAME="GENERATOR" CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK REV="MADE" HREF="mailto:pgsql-docs@postgresql.org"><LINK REL="HOME" TITLE="PostgreSQL 8.0.11 Documentation" HREF="index.html"><LINK REL="UP" TITLE="Client Interfaces" HREF="client-interfaces.html"><LINK REL="PREVIOUS" TITLE="Client Interfaces" HREF="client-interfaces.html"><LINK REL="NEXT" TITLE="Connection Status Functions" HREF="libpq-status.html"><LINK REL="STYLESHEET" TYPE="text/css" HREF="stylesheet.css"><META HTTP-EQUIV="Content-Type" CONTENT="text/html; charset=ISO-8859-1"><META NAME="creation" CONTENT="2007-02-02T03:57:22"></HEAD ><BODY CLASS="CHAPTER" ><DIV CLASS="NAVHEADER" ><TABLE SUMMARY="Header navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TH COLSPAN="5" ALIGN="center" VALIGN="bottom" >PostgreSQL 8.0.11 Documentation</TH ></TR ><TR ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="client-interfaces.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="10%" ALIGN="left" VALIGN="top" ><A HREF="client-interfaces.html#AEN22500" >Fast Backward</A ></TD ><TD WIDTH="60%" ALIGN="center" VALIGN="bottom" ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="top" ><A HREF="largeobjects.html" >Fast Forward</A ></TD ><TD WIDTH="10%" ALIGN="right" VALIGN="top" ><A HREF="libpq-status.html" ACCESSKEY="N" >Next</A ></TD ></TR ></TABLE ><HR ALIGN="LEFT" WIDTH="100%"></DIV ><DIV CLASS="CHAPTER" ><H1 ><A NAME="LIBPQ" ></A >Chapter 27. <SPAN CLASS="APPLICATION" >libpq</SPAN > - C Library</H1 ><DIV CLASS="TOC" ><DL ><DT ><B >Table of Contents</B ></DT ><DT >27.1. <A HREF="libpq.html#LIBPQ-CONNECT" >Database Connection Control Functions</A ></DT ><DT >27.2. <A HREF="libpq-status.html" >Connection Status Functions</A ></DT ><DT >27.3. <A HREF="libpq-exec.html" >Command Execution Functions</A ></DT ><DD ><DL ><DT >27.3.1. <A HREF="libpq-exec.html#LIBPQ-EXEC-MAIN" >Main Functions</A ></DT ><DT >27.3.2. <A HREF="libpq-exec.html#LIBPQ-EXEC-SELECT-INFO" >Retrieving Query Result Information</A ></DT ><DT >27.3.3. <A HREF="libpq-exec.html#LIBPQ-EXEC-NONSELECT" >Retrieving Result Information for Other Commands</A ></DT ><DT >27.3.4. <A HREF="libpq-exec.html#LIBPQ-EXEC-ESCAPE-STRING" >Escaping Strings for Inclusion in SQL Commands</A ></DT ><DT >27.3.5. <A HREF="libpq-exec.html#LIBPQ-EXEC-ESCAPE-BYTEA" >Escaping Binary Strings for Inclusion in SQL Commands</A ></DT ></DL ></DD ><DT >27.4. <A HREF="libpq-async.html" >Asynchronous Command Processing</A ></DT ><DT >27.5. <A HREF="libpq-cancel.html" >Cancelling Queries in Progress</A ></DT ><DT >27.6. <A HREF="libpq-fastpath.html" >The Fast-Path Interface</A ></DT ><DT >27.7. <A HREF="libpq-notify.html" >Asynchronous Notification</A ></DT ><DT >27.8. <A HREF="libpq-copy.html" >Functions Associated with the <TT CLASS="COMMAND" >COPY</TT > Command</A ></DT ><DD ><DL ><DT >27.8.1. <A HREF="libpq-copy.html#LIBPQ-COPY-SEND" >Functions for Sending <TT CLASS="COMMAND" >COPY</TT > Data</A ></DT ><DT >27.8.2. <A HREF="libpq-copy.html#LIBPQ-COPY-RECEIVE" >Functions for Receiving <TT CLASS="COMMAND" >COPY</TT > Data</A ></DT ><DT >27.8.3. <A HREF="libpq-copy.html#LIBPQ-COPY-DEPRECATED" >Obsolete Functions for <TT CLASS="COMMAND" >COPY</TT ></A ></DT ></DL ></DD ><DT >27.9. <A HREF="libpq-control.html" >Control Functions</A ></DT ><DT >27.10. <A HREF="libpq-notice-processing.html" >Notice Processing</A ></DT ><DT >27.11. <A HREF="libpq-envars.html" >Environment Variables</A ></DT ><DT >27.12. <A HREF="libpq-pgpass.html" >The Password File</A ></DT ><DT >27.13. <A HREF="libpq-ssl.html" >SSL Support</A ></DT ><DT >27.14. <A HREF="libpq-threading.html" >Behavior in Threaded Programs</A ></DT ><DT >27.15. <A HREF="libpq-build.html" >Building <SPAN CLASS="APPLICATION" >libpq</SPAN > Programs</A ></DT ><DT >27.16. <A HREF="libpq-example.html" >Example Programs</A ></DT ></DL ></DIV ><A NAME="AEN22509" ></A ><A NAME="AEN22511" ></A ><P > <SPAN CLASS="APPLICATION" >libpq</SPAN > is the <ACRONYM CLASS="ACRONYM" >C</ACRONYM > application programmer's interface to <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN >. <SPAN CLASS="APPLICATION" >libpq</SPAN > is a set of library functions that allow client programs to pass queries to the <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN > backend server and to receive the results of these queries. </P ><P > <SPAN CLASS="APPLICATION" >libpq</SPAN > is also the underlying engine for several other <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN > application interfaces, including those written for C++, Perl, Python, Tcl and <SPAN CLASS="APPLICATION" >ECPG</SPAN >. So some aspects of <SPAN CLASS="APPLICATION" >libpq</SPAN >'s behavior will be important to you if you use one of those packages. In particular, <A HREF="libpq-envars.html" >Section 27.11</A >, <A HREF="libpq-pgpass.html" >Section 27.12</A > and <A HREF="libpq-ssl.html" >Section 27.13</A > describe behavior that is visible to the user of any application that uses <SPAN CLASS="APPLICATION" >libpq</SPAN >. </P ><P > Some short programs are included at the end of this chapter (<A HREF="libpq-example.html" >Section 27.16</A >) to show how to write programs that use <SPAN CLASS="APPLICATION" >libpq</SPAN >. There are also several complete examples of <SPAN CLASS="APPLICATION" >libpq</SPAN > applications in the directory <TT CLASS="FILENAME" >src/test/examples</TT > in the source code distribution. </P ><P > Client programs that use <SPAN CLASS="APPLICATION" >libpq</SPAN > must include the header file <TT CLASS="FILENAME" >libpq-fe.h</TT ><A NAME="AEN22536" ></A > and must link with the <SPAN CLASS="APPLICATION" >libpq</SPAN > library. </P ><DIV CLASS="SECT1" ><H1 CLASS="SECT1" ><A NAME="LIBPQ-CONNECT" >27.1. Database Connection Control Functions</A ></H1 ><P > The following functions deal with making a connection to a <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN > backend server. An application program can have several backend connections open at one time. (One reason to do that is to access more than one database.) Each connection is represented by a <TT CLASS="STRUCTNAME" >PGconn</TT ><A NAME="AEN22544" ></A > object, which is obtained from the function <CODE CLASS="FUNCTION" >PQconnectdb</CODE > or <CODE CLASS="FUNCTION" >PQsetdbLogin</CODE >. Note that these functions will always return a non-null object pointer, unless perhaps there is too little memory even to allocate the <TT CLASS="STRUCTNAME" >PGconn</TT > object. The <CODE CLASS="FUNCTION" >PQstatus</CODE > function should be called to check whether a connection was successfully made before queries are sent via the connection object. <P ></P ></P><DIV CLASS="VARIABLELIST" ><DL ><DT ><CODE CLASS="FUNCTION" >PQconnectdb</CODE ><A NAME="AEN22554" ></A ></DT ><DD ><P > Makes a new connection to the database server. </P><PRE CLASS="SYNOPSIS" >PGconn *PQconnectdb(const char *conninfo);</PRE ><P></P ><P > This function opens a new database connection using the parameters taken from the string <TT CLASS="LITERAL" >conninfo</TT >. Unlike <CODE CLASS="FUNCTION" >PQsetdbLogin</CODE > below, the parameter set can be extended without changing the function signature, so use of this function (or its nonblocking analogues <CODE CLASS="FUNCTION" >PQconnectStart</CODE > and <CODE CLASS="FUNCTION" >PQconnectPoll</CODE >) is preferred for new application programming. </P ><P > The passed string can be empty to use all default parameters, or it can contain one or more parameter settings separated by whitespace. Each parameter setting is in the form <TT CLASS="LITERAL" >keyword = value</TT >. Spaces around the equal sign are optional. To write an empty value or a value containing spaces, surround it with single quotes, e.g., <TT CLASS="LITERAL" >keyword = 'a value'</TT >. Single quotes and backslashes within the value must be escaped with a backslash, i.e., <TT CLASS="LITERAL" >\'</TT > and <TT CLASS="LITERAL" >\\</TT >. </P ><P > The currently recognized parameter key words are: <P ></P ></P><DIV CLASS="VARIABLELIST" ><DL ><DT ><TT CLASS="LITERAL" >host</TT ></DT ><DD ><P > Name of host to connect to.<A NAME="AEN22576" ></A > If this begins with a slash, it specifies Unix-domain communication rather than TCP/IP communication; the value is the name of the directory in which the socket file is stored. The default behavior when <TT CLASS="LITERAL" >host</TT > is not specified is to connect to a Unix-domain socket<A NAME="AEN22579" ></A > in <TT CLASS="FILENAME" >/tmp</TT > (or whatever socket directory was specified when <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN > was built). On machines without Unix-domain sockets, the default is to connect to <TT CLASS="LITERAL" >localhost</TT >. </P ></DD ><DT ><TT CLASS="LITERAL" >hostaddr</TT ></DT ><DD ><P > Numeric IP address of host to connect to. This should be in the standard IPv4 address format, e.g., <TT CLASS="LITERAL" >172.28.40.9</TT >. If your machine supports IPv6, you can also use those addresses. TCP/IP communication is always used when a nonempty string is specified for this parameter. </P ><P > Using <TT CLASS="LITERAL" >hostaddr</TT > instead of <TT CLASS="LITERAL" >host</TT > allows the application to avoid a host name look-up, which may be important in applications with time constraints. However, Kerberos authentication requires the host name. The following therefore applies: If <TT CLASS="LITERAL" >host</TT > is specified without <TT CLASS="LITERAL" >hostaddr</TT >, a host name lookup occurs. If <TT CLASS="LITERAL" >hostaddr</TT > is specified without <TT CLASS="LITERAL" >host</TT >, the value for <TT CLASS="LITERAL" >hostaddr</TT > gives the remote address. When Kerberos is used, a reverse name query occurs to obtain the host name for Kerberos. If both <TT CLASS="LITERAL" >host</TT > and <TT CLASS="LITERAL" >hostaddr</TT > are specified, the value for <TT CLASS="LITERAL" >hostaddr</TT > gives the remote address; the value for <TT CLASS="LITERAL" >host</TT > is ignored, unless Kerberos is used, in which case that value is used for Kerberos authentication. (Note that authentication is likely to fail if <SPAN CLASS="APPLICATION" >libpq</SPAN > is passed a host name that is not the name of the machine at <TT CLASS="LITERAL" >hostaddr</TT >.) Also, <TT CLASS="LITERAL" >host</TT > rather than <TT CLASS="LITERAL" >hostaddr</TT > is used to identify the connection in <TT CLASS="FILENAME" >~/.pgpass</TT > (see <A HREF="libpq-pgpass.html" >Section 27.12</A >). </P ><P > Without either a host name or host address, <SPAN CLASS="APPLICATION" >libpq</SPAN > will connect using a local Unix-domain socket; or on machines without Unix-domain sockets, it will attempt to connect to <TT CLASS="LITERAL" >localhost</TT >. </P ></DD ><DT ><TT CLASS="LITERAL" >port</TT ></DT ><DD ><P > Port number to connect to at the server host, or socket file name extension for Unix-domain connections.<A NAME="AEN22616" ></A > </P ></DD ><DT ><TT CLASS="LITERAL" >dbname</TT ></DT ><DD ><P > The database name. Defaults to be the same as the user name. </P ></DD ><DT ><TT CLASS="LITERAL" >user</TT ></DT ><DD ><P > <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN > user name to connect as. Defaults to be the same as the operating system name of the user running the application. </P ></DD ><DT ><TT CLASS="LITERAL" >password</TT ></DT ><DD ><P > Password to be used if the server demands password authentication. </P ></DD ><DT ><TT CLASS="LITERAL" >connect_timeout</TT ></DT ><DD ><P > Maximum wait for connection, in seconds (write as a decimal integer string). Zero or not specified means wait indefinitely. It is not recommended to use a timeout of less than 2 seconds. </P ></DD ><DT ><TT CLASS="LITERAL" >options</TT ></DT ><DD ><P > Command-line options to be sent to the server. </P ></DD ><DT ><TT CLASS="LITERAL" >tty</TT ></DT ><DD ><P > Ignored (formerly, this specified where to send server debug output). </P ></DD ><DT ><TT CLASS="LITERAL" >sslmode</TT ></DT ><DD ><P > This option determines whether or with what priority an <ACRONYM CLASS="ACRONYM" >SSL</ACRONYM > connection will be negotiated with the server. There are four modes: <TT CLASS="LITERAL" >disable</TT > will attempt only an unencrypted <ACRONYM CLASS="ACRONYM" >SSL</ACRONYM > connection; <TT CLASS="LITERAL" >allow</TT > will negotiate, trying first a non-<ACRONYM CLASS="ACRONYM" >SSL</ACRONYM > connection, then if that fails, trying an <ACRONYM CLASS="ACRONYM" >SSL</ACRONYM > connection; <TT CLASS="LITERAL" >prefer</TT > (the default) will negotiate, trying first an <ACRONYM CLASS="ACRONYM" >SSL</ACRONYM > connection, then if that fails, trying a regular non-<ACRONYM CLASS="ACRONYM" >SSL</ACRONYM > connection; <TT CLASS="LITERAL" >require</TT > will try only an <ACRONYM CLASS="ACRONYM" >SSL</ACRONYM > connection. </P ><P > If <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN > is compiled without SSL support, using option <TT CLASS="LITERAL" >require</TT > will cause an error, while options <TT CLASS="LITERAL" >allow</TT > and <TT CLASS="LITERAL" >prefer</TT > will be accepted but <SPAN CLASS="APPLICATION" >libpq</SPAN > will not in fact attempt an <ACRONYM CLASS="ACRONYM" >SSL</ACRONYM > connection.<A NAME="AEN22672" ></A > </P ></DD ><DT ><TT CLASS="LITERAL" >requiressl</TT ></DT ><DD ><P > This option is deprecated in favor of the <TT CLASS="LITERAL" >sslmode</TT > setting. </P ><P > If set to 1, an <ACRONYM CLASS="ACRONYM" >SSL</ACRONYM > connection to the server is required (this is equivalent to <TT CLASS="LITERAL" >sslmode</TT > <TT CLASS="LITERAL" >require</TT >). <SPAN CLASS="APPLICATION" >libpq</SPAN > will then refuse to connect if the server does not accept an <ACRONYM CLASS="ACRONYM" >SSL</ACRONYM > connection. If set to 0 (default), <SPAN CLASS="APPLICATION" >libpq</SPAN > will negotiate the connection type with the server (equivalent to <TT CLASS="LITERAL" >sslmode</TT > <TT CLASS="LITERAL" >prefer</TT >). This option is only available if <SPAN CLASS="PRODUCTNAME" >PostgreSQL</SPAN > is compiled with SSL support. </P ></DD ><DT ><TT CLASS="LITERAL" >service</TT ></DT ><DD ><P > Service name to use for additional parameters. It specifies a service name in <TT CLASS="FILENAME" >pg_service.conf</TT > that holds additional connection parameters. This allows applications to specify only a service name so connection parameters can be centrally maintained. See <TT CLASS="FILENAME" >share/pg_service.conf.sample</TT > in the installation directory for information on how to set up the file. </P ></DD ></DL ></DIV ><P> If any parameter is unspecified, then the corresponding environment variable (see <A HREF="libpq-envars.html" >Section 27.11</A >) is checked. If the environment variable is not set either, then the indicated built-in defaults are used. </P ></DD ><DT ><CODE CLASS="FUNCTION" >PQsetdbLogin</CODE ><A NAME="AEN22702" ></A ></DT ><DD ><P > Makes a new connection to the database server. </P><PRE CLASS="SYNOPSIS" >PGconn *PQsetdbLogin(const char *pghost, const char *pgport, const char *pgoptions, const char *pgtty, const char *dbName, const char *login, const char *pwd);</PRE ><P></P ><P > This is the predecessor of <CODE CLASS="FUNCTION" >PQconnectdb</CODE > with a fixed set of parameters. It has the same functionality except that the missing parameters will always take on default values. Write <TT CLASS="SYMBOL" >NULL</TT > or an empty string for any one of the fixed parameters that is to be defaulted. </P ></DD ><DT ><CODE CLASS="FUNCTION" >PQsetdb</CODE ><A NAME="AEN22713" ></A ></DT ><DD ><P > Makes a new connection to the database server. </P><PRE CLASS="SYNOPSIS" >PGconn *PQsetdb(char *pghost, char *pgport, char *pgoptions, char *pgtty, char *dbName);</PRE ><P></P ><P > This is a macro that calls <CODE CLASS="FUNCTION" >PQsetdbLogin</CODE > with null pointers for the <TT CLASS="PARAMETER" >login</TT > and <TT CLASS="PARAMETER" >pwd</TT > parameters. It is provided for backward compatibility with very old programs. </P ></DD ><DT ><CODE CLASS="FUNCTION" >PQconnectStart</CODE ><A NAME="AEN22725" ></A ><BR><CODE CLASS="FUNCTION" >PQconnectPoll</CODE ><A NAME="AEN22729" ></A ></DT ><DD ><P > <A NAME="AEN22733" ></A > Make a connection to the database server in a nonblocking manner. </P><PRE CLASS="SYNOPSIS" >PGconn *PQconnectStart(const char *conninfo);</PRE ><P> </P><PRE CLASS="SYNOPSIS" >PostgresPollingStatusType PQconnectPoll(PGconn *conn);</PRE ><P></P ><P > These two functions are used to open a connection to a database server such that your application's thread of execution is not blocked on remote I/O whilst doing so. The point of this approach is that the waits for I/O to complete can occur in the application's main loop, rather than down inside <CODE CLASS="FUNCTION" >PQconnectdb</CODE >, and so the application can manage this operation in parallel with other activities. </P ><P > The database connection is made using the parameters taken from the string <TT CLASS="LITERAL" >conninfo</TT >, passed to <CODE CLASS="FUNCTION" >PQconnectStart</CODE >. This string is in the same format as described above for <CODE CLASS="FUNCTION" >PQconnectdb</CODE >. </P ><P > Neither <CODE CLASS="FUNCTION" >PQconnectStart</CODE > nor <CODE CLASS="FUNCTION" >PQconnectPoll</CODE > will block, so long as a number of restrictions are met: <P ></P ></P><UL ><LI ><P > The <TT CLASS="LITERAL" >hostaddr</TT > and <TT CLASS="LITERAL" >host</TT > parameters are used appropriately to ensure that name and reverse name queries are not made. See the documentation of these parameters under <CODE CLASS="FUNCTION" >PQconnectdb</CODE > above for details. </P ></LI ><LI ><P > If you call <CODE CLASS="FUNCTION" >PQtrace</CODE >, ensure that the stream object into which you trace will not block. </P ></LI ><LI ><P > You ensure that the socket is in the appropriate state before calling <CODE CLASS="FUNCTION" >PQconnectPoll</CODE >, as described below. </P ></LI ></UL ><P> </P ><P > To begin a nonblocking connection request, call <TT CLASS="LITERAL" >conn = PQconnectStart("<TT CLASS="REPLACEABLE" ><I >connection_info_string</I ></TT >")</TT >. If <TT CLASS="VARNAME" >conn</TT > is null, then <SPAN CLASS="APPLICATION" >libpq</SPAN > has been unable to allocate a new <TT CLASS="STRUCTNAME" >PGconn</TT > structure. Otherwise, a valid <TT CLASS="STRUCTNAME" >PGconn</TT > pointer is returned (though not yet representing a valid connection to the database). On return from <CODE CLASS="FUNCTION" >PQconnectStart</CODE >, call <TT CLASS="LITERAL" >status = PQstatus(conn)</TT >. If <TT CLASS="VARNAME" >status</TT > equals <TT CLASS="SYMBOL" >CONNECTION_BAD</TT >, <CODE CLASS="FUNCTION" >PQconnectStart</CODE > has failed. </P ><P > If <CODE CLASS="FUNCTION" >PQconnectStart</CODE > succeeds, the next stage is to poll <SPAN CLASS="APPLICATION" >libpq</SPAN > so that it may proceed with the connection sequence. Use <CODE CLASS="FUNCTION" >PQsocket(conn)</CODE > to obtain the descriptor of the socket underlying the database connection. Loop thus: If <CODE CLASS="FUNCTION" >PQconnectPoll(conn)</CODE > last returned <TT CLASS="SYMBOL" >PGRES_POLLING_READING</TT >, wait until the socket is ready to read (as indicated by <CODE CLASS="FUNCTION" >select()</CODE >, <CODE CLASS="FUNCTION" >poll()</CODE >, or similar system function). Then call <CODE CLASS="FUNCTION" >PQconnectPoll(conn)</CODE > again. Conversely, if <CODE CLASS="FUNCTION" >PQconnectPoll(conn)</CODE > last returned <TT CLASS="SYMBOL" >PGRES_POLLING_WRITING</TT >, wait until the socket is ready to write, then call <CODE CLASS="FUNCTION" >PQconnectPoll(conn)</CODE > again. If you have yet to call <CODE CLASS="FUNCTION" >PQconnectPoll</CODE >, i.e., just after the call to <CODE CLASS="FUNCTION" >PQconnectStart</CODE >, behave as if it last returned <TT CLASS="SYMBOL" >PGRES_POLLING_WRITING</TT >. Continue this loop until <CODE CLASS="FUNCTION" >PQconnectPoll(conn)</CODE > returns <TT CLASS="SYMBOL" >PGRES_POLLING_FAILED</TT >, indicating the connection procedure has failed, or <TT CLASS="SYMBOL" >PGRES_POLLING_OK</TT >, indicating the connection has been successfully made. </P ><P > At any time during connection, the status of the connection may be checked by calling <CODE CLASS="FUNCTION" >PQstatus</CODE >. If this gives <TT CLASS="SYMBOL" >CONNECTION_BAD</TT >, then the connection procedure has failed; if it gives <CODE CLASS="FUNCTION" >CONNECTION_OK</CODE >, then the connection is ready. Both of these states are equally detectable from the return value of <CODE CLASS="FUNCTION" >PQconnectPoll</CODE >, described above. Other states may also occur during (and only during) an asynchronous connection procedure. These indicate the current stage of the connection procedure and may be useful to provide feedback to the user for example. These statuses are: <P ></P ></P><DIV CLASS="VARIABLELIST" ><DL ><DT ><TT CLASS="SYMBOL" >CONNECTION_STARTED</TT ></DT ><DD ><P > Waiting for connection to be made. </P ></DD ><DT ><TT CLASS="SYMBOL" >CONNECTION_MADE</TT ></DT ><DD ><P > Connection OK; waiting to send. </P ></DD ><DT ><TT CLASS="SYMBOL" >CONNECTION_AWAITING_RESPONSE</TT ></DT ><DD ><P > Waiting for a response from the server. </P ></DD ><DT ><TT CLASS="SYMBOL" >CONNECTION_AUTH_OK</TT ></DT ><DD ><P > Received authentication; waiting for backend start-up to finish. </P ></DD ><DT ><TT CLASS="SYMBOL" >CONNECTION_SSL_STARTUP</TT ></DT ><DD ><P > Negotiating SSL encryption. </P ></DD ><DT ><TT CLASS="SYMBOL" >CONNECTION_SETENV</TT ></DT ><DD ><P > Negotiating environment-driven parameter settings. </P ></DD ></DL ></DIV ><P> Note that, although these constants will remain (in order to maintain compatibility), an application should never rely upon these occurring in a particular order, or at all, or on the status always being one of these documented values. An application might do something like this: </P><PRE CLASS="PROGRAMLISTING" >switch(PQstatus(conn)) { case CONNECTION_STARTED: feedback = "Connecting..."; break; case CONNECTION_MADE: feedback = "Connected to server..."; break; . . . default: feedback = "Connecting..."; }</PRE ><P> </P ><P > The <TT CLASS="LITERAL" >connect_timeout</TT > connection parameter is ignored when using <CODE CLASS="FUNCTION" >PQconnectPoll</CODE >; it is the application's responsibility to decide whether an excessive amount of time has elapsed. Otherwise, <CODE CLASS="FUNCTION" >PQconnectStart</CODE > followed by a <CODE CLASS="FUNCTION" >PQconnectPoll</CODE > loop is equivalent to <CODE CLASS="FUNCTION" >PQconnectdb</CODE >. </P ><P > Note that if <CODE CLASS="FUNCTION" >PQconnectStart</CODE > returns a non-null pointer, you must call <CODE CLASS="FUNCTION" >PQfinish</CODE > when you are finished with it, in order to dispose of the structure and any associated memory blocks. This must be done even if the connection attempt fails or is abandoned. </P ></DD ><DT ><CODE CLASS="FUNCTION" >PQconndefaults</CODE ><A NAME="AEN22837" ></A ></DT ><DD ><P > Returns the default connection options. </P><PRE CLASS="SYNOPSIS" >PQconninfoOption *PQconndefaults(void); typedef struct { char *keyword; /* The keyword of the option */ char *envvar; /* Fallback environment variable name */ char *compiled; /* Fallback compiled in default value */ char *val; /* Option's current value, or NULL */ char *label; /* Label for field in connect dialog */ char *dispchar; /* Character to display for this field in a connect dialog. Values are: "" Display entered value as is "*" Password field - hide value "D" Debug option - don't show by default */ int dispsize; /* Field size in characters for dialog */ } PQconninfoOption;</PRE ><P></P ><P > Returns a connection options array. This may be used to determine all possible <CODE CLASS="FUNCTION" >PQconnectdb</CODE > options and their current default values. The return value points to an array of <TT CLASS="STRUCTNAME" >PQconninfoOption</TT > structures, which ends with an entry having a null <TT CLASS="STRUCTFIELD" >keyword</TT > pointer. Note that the current default values (<TT CLASS="STRUCTFIELD" >val</TT > fields) will depend on environment variables and other context. Callers must treat the connection options data as read-only. </P ><P > After processing the options array, free it by passing it to <CODE CLASS="FUNCTION" >PQconninfoFree</CODE >. If this is not done, a small amount of memory is leaked for each call to <CODE CLASS="FUNCTION" >PQconndefaults</CODE >. </P ></DD ><DT ><CODE CLASS="FUNCTION" >PQfinish</CODE ><A NAME="AEN22853" ></A ></DT ><DD ><P > Closes the connection to the server. Also frees memory used by the <TT CLASS="STRUCTNAME" >PGconn</TT > object. </P><PRE CLASS="SYNOPSIS" >void PQfinish(PGconn *conn);</PRE ><P></P ><P > Note that even if the server connection attempt fails (as indicated by <CODE CLASS="FUNCTION" >PQstatus</CODE >), the application should call <CODE CLASS="FUNCTION" >PQfinish</CODE > to free the memory used by the <TT CLASS="STRUCTNAME" >PGconn</TT > object. The <TT CLASS="STRUCTNAME" >PGconn</TT > pointer must not be used again after <CODE CLASS="FUNCTION" >PQfinish</CODE > has been called. </P ></DD ><DT ><CODE CLASS="FUNCTION" >PQreset</CODE ><A NAME="AEN22868" ></A ></DT ><DD ><P > Resets the communication channel to the server. </P><PRE CLASS="SYNOPSIS" >void PQreset(PGconn *conn);</PRE ><P></P ><P > This function will close the connection to the server and attempt to reestablish a new connection to the same server, using all the same parameters previously used. This may be useful for error recovery if a working connection is lost. </P ></DD ><DT ><CODE CLASS="FUNCTION" >PQresetStart</CODE ><A NAME="AEN22877" ></A ><BR><CODE CLASS="FUNCTION" >PQresetPoll</CODE ><A NAME="AEN22881" ></A ></DT ><DD ><P > Reset the communication channel to the server, in a nonblocking manner. </P><PRE CLASS="SYNOPSIS" >int PQresetStart(PGconn *conn);</PRE ><P> </P><PRE CLASS="SYNOPSIS" >PostgresPollingStatusType PQresetPoll(PGconn *conn);</PRE ><P></P ><P > These functions will close the connection to the server and attempt to reestablish a new connection to the same server, using all the same parameters previously used. This may be useful for error recovery if a working connection is lost. They differ from <CODE CLASS="FUNCTION" >PQreset</CODE > (above) in that they act in a nonblocking manner. These functions suffer from the same restrictions as <CODE CLASS="FUNCTION" >PQconnectStart</CODE > and <CODE CLASS="FUNCTION" >PQconnectPoll</CODE >. </P ><P > To initiate a connection reset, call <CODE CLASS="FUNCTION" >PQresetStart</CODE >. If it returns 0, the reset has failed. If it returns 1, poll the reset using <CODE CLASS="FUNCTION" >PQresetPoll</CODE > in exactly the same way as you would create the connection using <CODE CLASS="FUNCTION" >PQconnectPoll</CODE >. </P ></DD ></DL ></DIV ><P></P ></DIV ></DIV ><DIV CLASS="NAVFOOTER" ><HR ALIGN="LEFT" WIDTH="100%"><TABLE SUMMARY="Footer navigation table" WIDTH="100%" BORDER="0" CELLPADDING="0" CELLSPACING="0" ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" ><A HREF="client-interfaces.html" ACCESSKEY="P" >Prev</A ></TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="index.html" ACCESSKEY="H" >Home</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" ><A HREF="libpq-status.html" ACCESSKEY="N" >Next</A ></TD ></TR ><TR ><TD WIDTH="33%" ALIGN="left" VALIGN="top" >Client Interfaces</TD ><TD WIDTH="34%" ALIGN="center" VALIGN="top" ><A HREF="client-interfaces.html" ACCESSKEY="U" >Up</A ></TD ><TD WIDTH="33%" ALIGN="right" VALIGN="top" >Connection Status Functions</TD ></TR ></TABLE ></DIV ></BODY ></HTML >