libpq中调用prepared statement:

代码如下：

[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()

{

 int   nFields;

 int   i,

       j;



#ifdef DEBUG

 FILE    *debug;

#endif  /* DEBUG */



 PGconn    *conn;

 PGresult   *res;



 const char *conninfo="postgresql://postgres:postgres@localhost:5432/postgres";



 /* make a connection to the database */

 conn = PQconnectdb(conninfo);



 /* check to see that the backend connection was successfully made */

 if (PQstatus(conn) == CONNECTION_BAD)

 {

  fprintf(stderr, "Connection to database failed.\n");

  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);

 }



 PQclear(res);



 ////////////////////////////////////////////////////////////////////////////////////

 const char *stmt_name = "test_stmt";

 const char *stmt = "select * from customers where cust_id=$1";



 Oid param_types[1];

 param_types[0] = 0; ///let db to judge it.



 res = PQprepare(conn, stmt_name, stmt,1,param_types);

 if (PQresultStatus(res) != PGRES_COMMAND_OK)

 {

  fprintf(stderr, "PQprepare failed\n");

  PQclear(res);

  exit_nicely(conn);

 }



 PQclear(res);



 const char* custid = "3";

 const char* param_values[1];

 param_values[0] =custid;



 int param_lengths[1];

 param_lengths[0] = 1;



 int param_formats[1];

 param_formats[0] = 0;

 

 res = PQexecPrepared(conn, stmt_name, 1, param_values, param_lengths,

                        param_formats, 0);



 if (PQresultStatus(res) != PGRES_TUPLES_OK)

 {

  fprintf(stderr, "PQexecPrepared statement 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);



 /* 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：

[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

cust_id        cust_name      



3              Taylor         

[root@lex tst]#