libpq.3

.\" This is -*-nroff-*-
.\" XXX standard disclaimer belongs here....
.\" $Header: /cvsroot/pgsql/src/man/Attic/libpq.3,v 1.13 1998/03/23 15:09:30 momjian Exp $
.TH LIBPQ INTRO 03/12/94 PostgreSQL PostgreSQL
.SH DESCRIPTION
Libpq is the programmer's interface to Postgres.  Libpq is a set of
library routines that allows queries to pass to the Postgres backend and
instances to return through an IPC channel.
.PP
This version of the documentation describes the C interface library.
Three short programs are included at the end of this section to show how
to write programs that use Libpq.
.PP
There are several examples of Libpq applications in the following
directories:
.nf
\&../src/test/regress
\&../src/test/examples
\&../src/bin/psql
.fi
.PP
Frontend programs which use Libpq must include the header file
.B "libpq-fe.h"
and must link with the
.B libpq 
library.
.SH "Control and Initialization"
.PP
The following environment variables can be used to set up default
environment values to avoid hard-coding database names into
an application program:
.sp
\(bu
.B PGHOST
sets the default server name.
If it is set to a non-zero-length string, it causes TCP/IP
communication to be used, rather than the default local Unix domain sockets.
.sp
\(bu
.B PGOPTIONS
sets additional runtime options for the Postgres backend.
.sp
\(bu
.B PGPORT
sets the default port or local Unix domain socket file extension
for communicating with the Postgres backend.
.sp
\(bu
.B PGTTY
sets the file or tty on which debugging messages from the backend server
are displayed.
.sp
\(bu
.B PGDATABASE
sets the default Postgres database name.
.sp
\(bu
.B PGREALM
sets the
.I Kerberos
realm to use with Postgres, if it is different from the local realm.  If 
.B PGREALM
is set, Postgres applications will attempt authentication with servers
for this realm and use separate ticket files to avoid conflicts with
local ticket files.  This environment variable is only used if 
.I Kerberos
authentication is enabled.

.PP
The following environment variables can be used to specify user-level default behavior
for every Postgres session:
.sp
\(bu
.B PGDATESTYLE
sets the default style of date/time representation.
.sp
\(bu
.B PGTZ
sets the default time zone.

.PP
The following environment variables can be used to specify default internal
behavior for every Postgres session:
.sp
\(bu
.B PGGEQO
sets the default mode for the genetic optimizer.
.sp
\(bu
.B PGRPLANS
sets the default mode to allow or disable right-sided plans in the optimizer.
.sp
\(bu
.B PGCOSTHEAP
sets the default cost for heap searches for the optimizer.
.sp
\(bu
.B PGCOSTINDEX
sets the default cost for indexed searches for the optimizer.

.PP
See the
set(l)
man page for information on the arguments for these environment variables.

.SH "Database Connection Functions"
.PP
The following routines deal with making a connection to a backend
from a C program.
.PP
.B PQsetdb
.IP
Makes a new connection to a backend.
.nf
PGconn *PQsetdb(char *pghost,
                char *pgport,
                char *pgoptions,
                char *pgtty,
                char *dbName); 
.fi
If any argument is NULL, then the corresponding environment variable
is checked.  If the environment variable is also not set, then hardwired
defaults are used. 
.IP
.I PQsetdb
always returns a valid PGconn pointer.  The 
.I PQstatus
(see below) command should be called to ensure that a connection was
properly made before queries are sent via the connection.  Libpq
programmers should be careful to maintain the PGconn abstraction.  Use
the accessor functions below to get at the contents of PGconn.  Avoid
directly referencing the fields of the PGconn structure as they are
subject to change in the future.
.IP
.B PQdb
returns the database name of the connection.
.nf
char *PQdb(PGconn *conn)
.fi
.B PQhost
returns the host name of the connection.
.nf
char *PQhost(PGconn *conn)
.fi
.B PQoptions
returns the pgoptions used in the connection.
.nf
char *PQoptions(PGconn *conn)
.fi
.B PQport
returns the pgport of the connection.
.nf
char *PQport(PGconn *conn)
.fi
.B PQtty
returns the pgtty of the connection.
.nf
char *PQtty(PGconn *conn)
.fi
.B PQstatus
Returns the status of the connection. The status can be CONNECTION_OK or
CONNECTION_BAD.  
.nf
ConnStatusType *PQstatus(PGconn *conn)
.fi
.B PQerrorMessage
returns the error message associated with the connection
.nf
char *PQerrorMessage(PGconn* conn);
.fi
.PP
.B PQfinish
.IP
Close the connection to the backend.  Also frees memory used by the
PGconn structure.  The PGconn pointer should not be used after PQfinish
has been called. 
.nf
void PQfinish(PGconn *conn)
.fi
.PP
.B PQreset
.IP
Reset the communication port with the backend.  This function will close
the IPC socket connection to the backend and attempt to reestablish a
new connection to the same backend.
.nf
void PQreset(PGconn *conn)
.fi
.PP
.SH "Query Execution Functions"
.PP
.B PQexec
.IP
Submit a query to Postgres.  Returns a PGresult pointer if the query was
successful or a NULL otherwise.  If a NULL is returned, 
.I PQerrorMessage
can be used to get more information about the error.
.nf
PGresult *PQexec(PGconn *conn,
                 char *query);
.fi
The PGresult structure encapsulates the query result returned by the
backend.  Libpq programmers should be careful to maintain the PGresult
abstraction. Use the accessor functions described below to retrieve the
results of the query.  Avoid directly referencing the fields of the PGresult
structure as they are subject to change in the future. 
.PP
.B PQresultStatus
.IP
Returns the result status of the query.
.I PQresultStatus
can return one of the following values:
.nf
PGRES_EMPTY_QUERY,
PGRES_COMMAND_OK,  /* the query was a command */
PGRES_TUPLES_OK,  /* the query successfully returned tuples */
PGRES_COPY_OUT, 
PGRES_COPY_IN,
PGRES_BAD_RESPONSE, /* an unexpected response was received */
PGRES_NONFATAL_ERROR,
PGRES_FATAL_ERROR
.fi
.IP
If the result status is PGRES_TUPLES_OK, then the following routines can
be used to retrieve the tuples returned by the query.
.IP

.B PQntuples
returns the number of tuples (instances) in the query result.

.nf
int PQntuples(PGresult *res);
.fi

.B PQcmdTuples
returns the number of tuples (instances) affected by INSERT, UPDATE, and
DELETE queries.

.nf
char *PQcmdTuples(PGresult *res);
.fi

.B PQnfields
returns the number of fields (attributes) in the query result.
.nf
int PQnfields(PGresult *res);
.fi

.B PQfname
returns the field (attribute) name associated with the given field index.
Field indices start at 0.
.nf
char *PQfname(PGresult *res,
             int field_index);
.fi

.B PQfnumber
returns the field (attribute) index associated with the given field name.
.nf
int PQfnumber(PGresult *res,
             char* field_name);
.fi

.B PQftype
returns the field type associated with the given field index. The
integer returned is an internal coding of the type.  Field indices start
at 0.
.nf
Oid PQftype(PGresult *res,
            int field_num);
.fi

.B PQfsize
returns the size in bytes of the field associated with the given field
index. If the size returned is -1, the field is a variable length field.
Field indices start at 0. 
.nf
int2 PQfsize(PGresult *res,
             int field_index);
.fi

.B PQgetvalue
returns the field (attribute) value.  For most queries, the value
returned by 
.I PQgetvalue
is a null-terminated ASCII string representation
of the attribute value.  If the query was a result of a 
.B BINARY
cursor, then the value returned by
.I PQgetvalue
is the binary representation of the type in the internal format of the
backend server.  It is the programmer's responsibility to cast and
convert the data to the correct C type.  The value returned by 
.I PQgetvalue
points to storage that is part of the PGresult structure.  One must
explicitly copy the value into other storage if it is to be used past
the lifetime of the PGresult structure itself.
.nf
char* PQgetvalue(PGresult *res,
                 int tup_num,
                 int field_num);
.fi

.B PQgetlength
returns the length of a field (attribute) in bytes.  If the field
is a
.I "struct varlena" ,
the length returned here does 
.B not
include the size field of the varlena, i.e., it is 4 bytes less.
.nf
int PQgetlength(PGresult *res,
                int tup_num,
                int field_num);
.fi

.B PQgetisnull
returns the NULL status of a field.
.nf
int PQgetisnull(PGresult *res,
                int tup_num,
                int field_num);
.fi

.PP
.B PQcmdStatus
.IP 
Returns the command status associated with the last query command.
.nf
char *PQcmdStatus(PGresult *res);
.fi
.PP
.B PQoidStatus
.IP
Returns a string with the object id of the tuple inserted if the last
query is an INSERT command.  Otherwise, returns an empty string.
.nf
char* PQoidStatus(PGresult *res);
.fi
.PP
.B PQprint
.IP
+ Prints out all the tuples in an intelligent manner. The
.B psql
+ program uses this function for its output.
.nf
void PQprint(
      FILE* fout,      /* output stream */
      PGresult* res,   /* query results */
      PQprintOpt *ps   /* option structure */
        );

.fi
.I PQprintOpt
is a typedef'ed structure as defined below.
.(C
typedef struct _PQprintOpt {
    bool header;           /* print table headings and row count */
    bool align;            /* fill align the fields */
    bool standard;         /* old brain dead format (needs align) */
    bool html3;            /* output html3+ tables */
    bool expanded;         /* expand tables */
    bool pager;            /* use pager if needed */
    char *fieldSep;        /* field separator */
    char *caption;         /* html table caption (or NULL) */
    char **fieldName;      /* null terminated array of field names (or NULL) */
} PQprintOpt;
.fi
.LP
.B PQclear
.IP
Frees the storage associated with the PGresult.  Every query result
should be properly freed when it is no longer used.  Failure to do this
will result in memory leaks in the frontend application.  The PQresult*
passed in should be a value which is returned from PQexec().  Calling
PQclear() on an uninitialized PQresult pointer will very likely result
in a core dump. 
.nf
void PQclear(PQresult *res);
.fi
.PP
.SH "Fast Path"
.PP
Postgres provides a 
.B "fast path"
interface to send function calls to the backend.  This is a trapdoor
into system internals and can be a potential security hole.  Most users
will not need this feature. 
.nf
PGresult* PQfn(PGconn* conn,
	       int fnid, 
	       int *result_buf, 
	       int *result_len,
	       int result_is_int,
	       PQArgBlock *args, 
	       int nargs);
.fi
.PP
The
.I fnid
argument is the object identifier of the function to be executed.
.I result_buf
is the buffer in which to load the return value.  The caller must have
allocated sufficient space to store the return value.  
The result length will be returned in the storage pointed to by 
.I result_len.
If the result is to be an integer value, than 
.I result_is_int
should be set to 1; otherwise it should be set to 0.
.I args
and 
.I nargs
specify the arguments to the function.
.nf
typedef struct {
    int len;
    int isint;
    union {
        int *ptr;	
	int integer;
    } u;
} PQArgBlock;
.fi
.PP
.I PQfn
always returns a valid PGresult*.  The resultStatus should be checked
before the result is used.   The caller is responsible for freeing the
PGresult with 
.I PQclear
when it is not longer needed.
.PP
.SH "Asynchronous Notification"
.PP
Postgres supports asynchronous notification via the 
.I LISTEN
and
.I NOTIFY
commands.  A backend registers its interest in a particular relation
with the LISTEN command.  All backends listening on a particular
relation will be notified asynchronously when a NOTIFY of that relation
name is executed by another backend.  No additional information is
passed from the notifier to the listener.  Thus, typically, any actual
data that needs to be communicated is transferred through the relation.
.PP
Libpq applications are notified whenever a connected backend has
received an asynchronous notification.  However, the communication from
the backend to the frontend is not asynchronous.  Notification comes
piggy-backed on other query results.  Thus, an application must submit
queries, even empty ones, in order to receive notice of backend
notification.  In effect, the Libpq application must poll the backend to
see if there is any pending notification information.  After the
execution of a query, a frontend may call 
.I PQNotifies
to see if any notification data is available from the backend. 
.PP
.B PQNotifies
.IP
returns the notification from a list of unhandled notifications from the
backend. Returns NULL if there are no pending notifications from the
backend.   
.I PQNotifies
behaves like the popping of a stack.  Once a notification is returned
from
.I PQnotifies,
it is considered handled and will be removed from the list of
notifications.
.nf
PGnotify* PQNotifies(PGconn *conn);
.fi
.PP
The second sample program gives an example of the use of asynchronous
notification.
.PP
.SH "Functions Associated with the COPY Command"
.PP
The
.I copy
command in Postgres has options to read from or write to the network
connection used by Libpq.  Therefore, functions are necessary to
access this network connection directly so applications may take full
advantage of this capability.
.PP
.B PQgetline
.IP
Reads a newline-terminated line of characters (transmitted by the
backend server) into a buffer 
.I string 
of size
.I length .
Like
.I fgets (3),
this routine copies up to 
.I length "-1"
characters into 
.I string .
It is like 
.I gets (3),
however, in that it converts the terminating newline into a null
character.
.IP
.I PQgetline
returns EOF at EOF, 0 if the entire line has been read, and 1 if the
buffer is full but the terminating newline has not yet been read.
.IP
Notice that the application must check to see if a new line consists
of the characters \*(lq\\.\*(rq, which indicates that the backend
server has finished sending the results of the 
.I copy
command.  Therefore, if the application ever expects to receive lines
that are more than
.I length "-1"
characters long, the application must be sure to check the return
value of 
.I PQgetline
very carefully.
.IP
The code in
.nf
\&../src/bin/psql/psql.c
.fi
contains routines that correctly handle the copy protocol.
.nf
int PQgetline(PGconn *conn,
              char *string,
              int length)
.fi
.PP
.B PQputline
.IP
Sends a null-terminated 
.I string
to the backend server.
.IP
The application must explicitly send the characters \*(lq\\.\*(rq
to indicate to the backend that it has finished sending its data.
.nf
void PQputline(PGconn *conn,
               char *string);
.fi
.PP
.B PQendcopy
.IP
Syncs with the backend.  This function waits until the backend has
finished the copy.  It should either be issued when the
last string has been sent to the backend using
.I PQputline
or when the last string has been received from the backend using
.I PGgetline .
It must be issued or the backend may get \*(lqout of sync\*(rq with
the frontend.  Upon return from this function, the backend is ready to
receive the next query.
.IP
The return value is 0 on successful completion, nonzero otherwise.
.nf
int PQendcopy(PGconn *conn);
.fi
As an example:
.nf
PQexec(conn, "create table foo (a int4, b char16, d float8)");
PQexec(conn, "copy foo from stdin");
PQputline(conn, "3<TAB>hello world<TAB>4.5\en");
PQputline(conn,"4<TAB>goodbye world<TAB>7.11\en");
\&...
PQputline(conn,"\\.\en");
PQendcopy(conn);
.fi
.PP
.SH "LIBPQ Tracing Functions"
.PP
.B PQtrace
.IP
Enable tracing of the frontend/backend communication to a debugging file
stream. 
.nf
void PQtrace(PGconn *conn
             FILE *debug_port)
.fi
.PP
.B PQuntrace 
.IP
Disable tracing started by 
.I PQtrace
.nf
void PQuntrace(PGconn *conn)
.fi
.PP
.SH "User Authentication Functions"
.PP
If the user has generated the appropriate authentication credentials
(e.g., obtaining
.I Kerberos
tickets), the frontend/backend authentication process is handled by
.I PQexec
without any further intervention.  The authentication method is now
determined entirely by the DBA (see pga_hba.conf(5)).  The following
routines no longer have any effect and should not be used.
.PP
.B fe_getauthname
.IP
Returns a pointer to static space containing whatever name the user
has authenticated.  Use of this routine in place of calls to
.I getenv (3)
or 
.I getpwuid (3)
by applications is highly recommended, as it is entirely possible that
the authenticated user name is 
.B not
the same as value of the
.B USER
environment variable or the user's entry in
.I /etc/passwd .
.nf
char *fe_getauthname(char* errorMessage)
.fi
.PP
.B fe_setauthsvc
.IP
Specifies that Libpq should use authentication service
.I name
rather than its compiled-in default.  This value is typically taken
from a command-line switch.
.nf
void fe_setauthsvc(char *name,
                   char* errorMessage)
.fi
Any error messages from the authentication attempts are returned in the
errorMessage argument.
.PP
.SH "BUGS"
.PP
The query buffer is 8192 bytes long, and queries over that length will
be silently truncated.
.PP
.SH "Sample Programs"
.bp
.SH "Sample Program 1"
.PP
.nf M
/*
 * testlibpq.c
 * 	Test the C version of Libpq, the Postgres frontend library.
 *
 *
 */
#include <stdio.h>
#include "libpq-fe.h"

void 
exit_nicely(PGconn* conn)
{
  PQfinish(conn);
  exit(1);
}

main()
{
  char *pghost, *pgport, *pgoptions, *pgtty;
  char* dbName;
  int nFields;
  int i,j;

/*  FILE *debug; */

  PGconn* conn;
  PGresult* res;

  /* begin, by setting the parameters for a backend connection
     if the parameters are null, then the system will try to use
     reasonable defaults by looking up environment variables 
     or, failing that, using hardwired constants */
  pghost = NULL;  /* host name of the backend server */
  pgport = NULL;  /* port of the backend server */
  pgoptions = NULL; /* special options to start up the backend server */
  pgtty = NULL;     /* debugging tty for the backend server */
  dbName = "template1";

  /* make a connection to the database */
  conn = PQsetdb(pghost, pgport, pgoptions, pgtty, dbName);

  /* check to see that the backend connection was successfully made */
  if (PQstatus(conn) == CONNECTION_BAD) {
    fprintf(stderr,"Connection to database '%s' failed.\\n", dbName);
    fprintf(stderr,"%s",PQerrorMessage(conn));
    exit_nicely(conn);
  }

/*  debug = fopen("/tmp/trace.out","w");  */
/*   PQtrace(conn, debug);  */

  /* start a transaction block */
  res = PQexec(conn,"BEGIN"); 
  if (PQresultStatus(res) != PGRES_COMMAND_OK) {
    fprintf(stderr,"BEGIN command failed\\n");
    PQclear(res);
    exit_nicely(conn);
  }
  /* should PQclear PGresult whenever it is no longer needed to avoid
     memory leaks */
  PQclear(res); 

  /* fetch instances from the pg_database, the system catalog of databases*/
  res = PQexec(conn,"DECLARE mycursor CURSOR FOR select * from pg_database");
  if (PQresultStatus(res) != PGRES_COMMAND_OK) {
    fprintf(stderr,"DECLARE CURSOR command failed\\n");
    PQclear(res);
    exit_nicely(conn);
  }
  PQclear(res);

  res = PQexec(conn,"FETCH ALL in mycursor");
  if (PQresultStatus(res) != PGRES_TUPLES_OK) {
    fprintf(stderr,"FETCH ALL command didn't return tuples properly\\n");
    PQclear(res);
    exit_nicely(conn);
  }
 
  /* first, print out the attribute names */
  nFields = PQnfields(res);
  for (i=0; i < nFields; i++) {
    printf("%-15s",PQfname(res,i));
  }
  printf("\\n\\n");

  /* next, print out the instances */
  for (i=0; i < PQntuples(res); i++) {
    for (j=0  ; j < nFields; j++) {
      printf("%-15s", PQgetvalue(res,i,j));
    }
    printf("\\n");
  }

  PQclear(res);
  
  /* close the cursor */
  res = PQexec(conn, "CLOSE mycursor");
  PQclear(res);

  /* commit the transaction */
  res = PQexec(conn, "COMMIT");
  PQclear(res);

  /* close the connection to the database and cleanup */
  PQfinish(conn);

/*   fclose(debug); */
}
.fi
.bp
.SH "Sample Program 2"
.PP
.nf M
/*
 * testlibpq2.c
 * 	Test of the asynchronous notification interface
 *
   populate a database with the following:

CREATE TABLE TBL1 (i int4);

CREATE TABLE TBL2 (i int4);

CREATE RULE r1 AS ON INSERT TO TBL1 DO [INSERT INTO TBL2 values (new.i); NOTIFY TBL2];

 * Then start up this program
 * After the program has begun, do

INSERT INTO TBL1 values (10);

 *
 *
 */
#include <stdio.h>
#include "libpq-fe.h"

void exit_nicely(PGconn* conn)
{
  PQfinish(conn);
  exit(1);
}

main()
{
  char *pghost, *pgport, *pgoptions, *pgtty;
  char* dbName;
  int nFields;
  int i,j;

  PGconn* conn;
  PGresult* res;
  PGnotify* notify;

  /* begin, by setting the parameters for a backend connection
     if the parameters are null, then the system will try to use
     reasonable defaults by looking up environment variables 
     or, failing that, using hardwired constants */
  pghost = NULL;  /* host name of the backend server */
  pgport = NULL;  /* port of the backend server */
  pgoptions = NULL; /* special options to start up the backend server */
  pgtty = NULL;     /* debugging tty for the backend server */
  dbName = getenv("USER"); /* change this to the name of your test database*/

  /* make a connection to the database */
  conn = PQsetdb(pghost, pgport, pgoptions, pgtty, dbName);

  /* check to see that the backend connection was successfully made */
  if (PQstatus(conn) == CONNECTION_BAD) {
    fprintf(stderr,"Connection to database '%s' failed.\\n", dbName);
    fprintf(stderr,"%s",PQerrorMessage(conn));
    exit_nicely(conn);
  }

  res = PQexec(conn, "LISTEN TBL2");
  if (PQresultStatus(res) != PGRES_COMMAND_OK) {
    fprintf(stderr,"LISTEN command failed\\n");
    PQclear(res);
    exit_nicely(conn);
  }
  /* should PQclear PGresult whenever it is no longer needed to avoid
     memory leaks */
  PQclear(res); 

  while (1) {
      /* async notification only come back as a result of a query*/
      /* we can send empty queries */
      res = PQexec(conn, "");
/*      printf("res->status = %s\\n", pgresStatus[PQresultStatus(res)]); */
      /* check for asynchronous returns */
      notify = PQnotifies(conn);
      if (notify) {
	  fprintf(stderr,
		  "ASYNC NOTIFY of '%s' from backend pid '%d' received\\n",
		  notify->relname, notify->be_pid);
	  free(notify);
	  break;
      }
      PQclear(res);
  }
      
  /* close the connection to the database and cleanup */
  PQfinish(conn);

}
.fi
.bp
.SH "Sample Program 3"
.PP
.nf M
/*
 * testlibpq3.c
 * 	Test the C version of Libpq, the Postgres frontend library.
 *   tests the binary cursor interface
 *
 *
 *
 populate a database by doing the following:
 
CREATE TABLE test1 (i int4, d float4, p polygon);

INSERT INTO test1 values (1, 3.567, '(3.0, 4.0, 1.0, 2.0)'::polygon);

INSERT INTO test1 values (2, 89.05, '(4.0, 3.0, 2.0, 1.0)'::polygon);

 the expected output is:

tuple 0: got
 i = (4 bytes) 1,
 d = (4 bytes) 3.567000,
 p = (4 bytes) 2 points         boundbox = (hi=3.000000/4.000000, lo = 1.000000,2.000000)
tuple 1: got
 i = (4 bytes) 2,
 d = (4 bytes) 89.050003,
 p = (4 bytes) 2 points         boundbox = (hi=4.000000/3.000000, lo = 2.000000,1.000000)

 *
 */
#include <stdio.h>
#include "libpq-fe.h"
#include "utils/geo-decls.h" /* for the POLYGON type */

void exit_nicely(PGconn* conn)
{
  PQfinish(conn);
  exit(1);
}

main()
{
  char *pghost, *pgport, *pgoptions, *pgtty;
  char* dbName;
  int nFields;
  int i,j;
  int i_fnum, d_fnum, p_fnum;

  PGconn* conn;
  PGresult* res;

  /* begin, by setting the parameters for a backend connection
     if the parameters are null, then the system will try to use
     reasonable defaults by looking up environment variables 
     or, failing that, using hardwired constants */
  pghost = NULL;  /* host name of the backend server */
  pgport = NULL;  /* port of the backend server */
  pgoptions = NULL; /* special options to start up the backend server */
  pgtty = NULL;     /* debugging tty for the backend server */

  dbName = getenv("USER");  /* change this to the name of your test database*/

  /* make a connection to the database */
  conn = PQsetdb(pghost, pgport, pgoptions, pgtty, dbName);

  /* check to see that the backend connection was successfully made */
  if (PQstatus(conn) == CONNECTION_BAD) {
    fprintf(stderr,"Connection to database '%s' failed.\\n", dbName);
    fprintf(stderr,"%s",PQerrorMessage(conn));
    exit_nicely(conn);
  }

  /* start a transaction block */
  res = PQexec(conn,"BEGIN"); 
  if (PQresultStatus(res) != PGRES_COMMAND_OK) {
    fprintf(stderr,"BEGIN command failed\\n");
    PQclear(res);
    exit_nicely(conn);
  }
  /* should PQclear PGresult whenever it is no longer needed to avoid
     memory leaks */
  PQclear(res); 

  /* fetch instances from the pg_database, the system catalog of databases*/
  res = PQexec(conn,"DECLARE mycursor BINARY CURSOR FOR select * from test1");
  if (PQresultStatus(res) != PGRES_COMMAND_OK) {
    fprintf(stderr,"DECLARE CURSOR command failed\\n");
    PQclear(res);
    exit_nicely(conn);
  }
  PQclear(res);

  res = PQexec(conn,"FETCH ALL in mycursor");
  if (PQresultStatus(res) != PGRES_TUPLES_OK) {
    fprintf(stderr,"FETCH ALL command didn't return tuples properly\\n");
    PQclear(res);
    exit_nicely(conn);
  }
 
  i_fnum = PQfnumber(res,"i");
  d_fnum = PQfnumber(res,"d");
  p_fnum = PQfnumber(res,"p");
  
  for (i=0;i<3;i++) {
      printf("type[%d] = %d, size[%d] = %d\\n",
	     i, PQftype(res,i), 
	     i, PQfsize(res,i));
  }
  for (i=0; i < PQntuples(res); i++) {
    int *ival; 
    float *dval;
    int plen;
    POLYGON* pval;
    /* we hard-wire this to the 3 fields we know about */
    ival =  (int*)PQgetvalue(res,i,i_fnum);
    dval =  (float*)PQgetvalue(res,i,d_fnum);
    plen = PQgetlength(res,i,p_fnum);

    /* plen doesn't include the length field so need to increment by VARHDSZ*/
    pval = (POLYGON*) malloc(plen + VARHDRSZ); 
    pval->size = plen;
    memmove((char*)&pval->npts, PQgetvalue(res,i,p_fnum), plen);
    printf("tuple %d: got\\n", i);
    printf(" i = (%d bytes) %d,\\n",
	   PQgetlength(res,i,i_fnum), *ival);
    printf(" d = (%d bytes) %f,\\n",
	   PQgetlength(res,i,d_fnum), *dval);
    printf(" p = (%d bytes) %d points \\tboundbox = (hi=%f/%f, lo = %f,%f)\\n",
	   PQgetlength(res,i,d_fnum),
	   pval->npts,
	   pval->boundbox.xh,
	   pval->boundbox.yh,
	   pval->boundbox.xl,
	   pval->boundbox.yl);
  }

  PQclear(res);
  
  /* close the cursor */
  res = PQexec(conn, "CLOSE mycursor");
  PQclear(res);

  /* commit the transaction */
  res = PQexec(conn, "COMMIT");
  PQclear(res);

  /* close the connection to the database and cleanup */
  PQfinish(conn);

}
.fi