连接PSQL数据库实例

#include <stdio.h>
        #include <stdlib.h>
        #include "libpq-fe.h"                                   /* libpq header file */
         
        int
        main()
        {
            char        state_code[3];                          /* holds user state code */
            char        query_string[256];                      /* holds constructed SQL query */
            PGconn     *conn;                                   /* holds database connection */
            PGresult   *res;                                    /* holds query result */
            int         i;
         
            conn = PQconnectdb("dbname=test");                  /* connect to the database */
         
            if (PQstatus(conn) == CONNECTION_BAD)               /* did the connection fail? */
            {
                fprintf(stderr, "Connection to database failed.\n");
                fprintf(stderr, "%s", PQerrorMessage(conn));
                exit(1);
            }
         
            printf("Enter a state code:  ");                    /* prompt user for a state code */
            scanf("%2s", state_code);
         
            sprintf(query_string,                               /* create an SQL query string */
                    "SELECT name \
                     FROM statename \
                     WHERE code = '%s'", state_code);