libpq程序例子

程序：

[root@lex tst]# cat testlibpq.c

/*

 * testlibpq.c

 *  Test the C version of LIBPQ, the POSTGRES frontend library.

 */

#include <stdio.h>

#include <stdlib.h>

#include "libpq-fe.h"



static void

exit_nicely(PGconn *conn)

{

 PQfinish(conn);

 exit(EXIT_SUCCESS);

}



int

main()

{

 char    *pghost,

         *pgport,

         *pgoptions,

         *pgtty;

 char    *dbName;

 int   nFields;

 int   i,

       j;



#ifdef DEBUG

 FILE    *debug;

#endif  /* DEBUG */



 PGconn    *conn;

 PGresult   *res;



 /*

  * Begin by setting the parameters for a backend connection.

  * If the parameters are NULL, the system tries to use 

  * reasonable defaults by looking up environment variables 

  * or, failing that, using hardwired constants.

  */



 const char *conninfo="postgresql://postgres:postgres@localhost:5432/postgres"; /* make a connection to the database */

 //conn = PQsetdb(pghost, pgport, pgoptions, pgtty, dbName);

 conn = PQconnectdb(conninfo);



 /* 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);

 }



#ifdef DEBUG

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

 PQtrace(conn, debug);

#endif  /* 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 

  * so as to avoid memory leaks

  */

 PQclear(res);



 /*

  * 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);



#ifdef DEBUG

 fclose(debug);

#endif  /* DEBUG */



 return 0;

}

[root@lex tst]# 

编译和运行：

export LD_LIBRARY_PATH=/usr/local/pgsql/lib

[root@lex tst]# gcc -c -I/usr/local/pgsql/include testlibpq.c

[root@lex tst]# gcc -o testlibpq testlibpq.o -L/usr/local/pgsql/lib -lpq

[root@lex tst]# ./testlibpq

datname        datdba         encoding       datcollate     datctype       datistemplate  datallowconn   datconnlimit   datlastsysoid  datfrozenxid   dattablespace  datacl         



template1      10             6              en_US.UTF-8    en_US.UTF-8    t              t              -1             12783          1672           1663           {=c/postgres,postgres=CTc/postgres}

template0      10             6              en_US.UTF-8    en_US.UTF-8    t              f              -1             12783          1672           1663           {=c/postgres,postgres=CTc/postgres}

postgres       10             6              en_US.UTF-8    en_US.UTF-8    f              t              -1             12783          1672           1663                          

[root@lex tst]#