ftp.nice.ch/pub/next/database/postgres95/postgres95Libs.NIHS.b.tar.gz#/postgres95Libs.pkg/_postgres95Libs/examples/testlibpq4.c

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/*
 * testlibpq4.c
 * 	this test programs shows to use LIBPQ to make multiple backend
 * connections
 *
 *
 */
#include <stdio.h>
#include "libpq-fe.h"

void 
exit_nicely(PGconn* conn1, PGconn* conn2)
{
    if (conn1)
	PQfinish(conn1);
    if (conn2)
	PQfinish(conn2);
    exit(1);
}

void check_conn(PGconn* conn)
{
  /* 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(1);
  }
}

main()
{
  char *pghost, *pgport, *pgoptions, *pgtty;
  char* dbName1, dbName2;
  char* tblName;
  int nFields;
  int i,j;

  PGconn* conn1, conn2;
  PGresult* res1, res2;

  if (argc != 4) 
      {
	  fprintf(stderr,"usage: %s tableName dbName1 dbName2\n",argv[0]);
	  fprintf(stderr,"      compares two tables in two databases\n");
	  exit(1);
      }
  tblName = argv[1];
  dbName1 = argv[2];
  dbName2 = argv[3];
  

  /* 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 */

  /* make a connection to the database */
  conn1 = PQsetdb(pghost, pgport, pgoptions, pgtty, dbName1);
  check_conn(conn1);

  conn2 = PQsetdb(pghost, pgport, pgoptions, pgtty, dbName2);
  check_conn(conn2);

  /* start a transaction block */
  res1 = PQexec(conn1,"BEGIN"); 
  if (PQresultStatus(res1) != PGRES_COMMAND_OK) {
    fprintf(stderr,"BEGIN command failed\n");
    PQclear(res1);
    exit_nicely(conn1,conn2);
  }
  /* should PQclear PGresult whenever it is no longer needed to avoid
     memory leaks */
  PQclear(res1); 

  /* fetch instances from the pg_database, the system catalog of databases*/
  res = PQexec(conn,"DECLARE myportal 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 myportal");
  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 portal */
  res = PQexec(conn, "CLOSE myportal");
  PQclear(res);

  /* end the transaction */
  res = PQexec(conn, "END");
  PQclear(res);

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

/*   fclose(debug); */
}
  

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