工作需要，虽然有libpqxx，但是目前为了刚刚够用，尽量不要引入第三方库。在网上找到简单的封装http://www.touspassagers.com/2010/12/a-postgresql-database-interface-wrapper-in-c/
直接贴上代码:
#include <iostream>
#include <stdio.h>
#include <string>
#include <stdlib.h>
#include <libpq-fe.h>
#include <map>
#include <math.h>
#include <string.h>
using namespace std;
typedef map<int,map<string,string> > map_result;
static void
finish_connection(PGconn conn)
{
PQfinish(conn);
}
class Conn
{
public:
// Methods
Conn(char connstring);
~Conn();
map_result fetch(char SQL);
int insert(char SQL);
void reset();
private:
// Members
PGconn conn;
const char conninfo;
PGresult res;
};
Conn::Conn(char connstring)
{
// Connect to the DB
conninfo = connstring;
conn = PQconnectdb(conninfo);
// See if the connection took:
if (PQstatus(conn) != CONNECTION_OK)
{
fprintf(stderr, “Could not connect to db/n%s”,
PQerrorMessage(conn));
finish_connection(conn);
}
}
Conn::~Conn()
{
finish_connection(conn);
}
void Conn::reset()
{
PQfinish(conn);
conn = PQconnectdb(conninfo);
}
map_result Conn::fetch(char SQL)
{
int row, col;
map_result results;
map<string,string> pairs;
// Check the connection:
if (PQstatus(conn) != CONNECTION_OK)
this->reset();
// Start a transaction:
res = PQexec(conn, “BEGIN”);
if (PQresultStatus(res) != PGRES_COMMAND_OK)
{
fprintf(stderr, “Failed to BEGIN transaction /n%s”,
PQerrorMessage(conn));
PQclear(res);
finish_connection(conn);
}
// Set up fetch query with a CURSOR:
string FinalSQL = string(“DECLARE myportal CURSOR FOR “) +
string(SQL);
// Declare CURSOR and execute query:
res = PQexec(conn,FinalSQL.c_str());
if (PQresultStatus(res) != PGRES_COMMAND_OK)
{
fprintf(stderr, “QUERY FAILED/n%s/n”,
PQerrorMessage(conn));
PQclear(res);
finish_connection(conn);
}
PQclear(res);
// Fetch results:
res = PQexec(conn, “FETCH ALL in myportal”);
if (PQresultStatus(res) != PGRES_TUPLES_OK)
{
fprintf(stderr, “FETCH ALL failed/n%s/n”,
PQerrorMessage(conn));
PQclear(res);
finish_connection(conn);
}
else
{
row = col = 0;
for (row=0; row<PQntuples(res); row++)
{
for(col=0; col<PQnfields(res); col++)
{
pairs[PQfname(res,col)] = PQgetvalue(res, row, col);
}
results[row] = pairs;
}
}
return results;
}
int Conn::insert(char sql)
{
// Check the connection:
if (PQstatus(conn) != CONNECTION_OK)
this->reset();
// Start a transaction:
res = PQexec(conn, “START TRANSACTION;”);
if (PQresultStatus(res) != PGRES_COMMAND_OK)
{
fprintf(stderr, “Failed to BEGIN transaction /n%s/n”,
PQerrorMessage(conn));
PQclear(res);
finish_connection(conn);
}
// Execute Insert:
res = PQexec(conn, sql);
if (PQresultStatus(res) != PGRES_COMMAND_OK)
{
fprintf(stderr, “Failed to execute INSERT /n%s/n”,
PQerrorMessage(conn));
PQclear(res);
finish_connection(conn);
}
// COMMIT transaction:
res = PQexec(conn, “COMMIT”);
if (PQresultStatus(res) != PGRES_COMMAND_OK)
{
fprintf(stderr, “Failed to COMMIT transaction/n%s/n”,
PQerrorMessage(conn));
PQclear(res);
finish_connection(conn);
}
return 0;
}
使用代码：
#include <iostream>
#include <boost/lexical_cast.hpp>
#include “PGConn.hpp”
using namespace std;
int main()
{
map_result res;
Conn postgres = new Conn(“dbname=mydb user=postgres”);
for( int i=0; i<10; ++i )
{
std::string strTemp( “(“ +boost::lexical_cast<std::string>(i) + “,” );
strTemp += boost::lexical_cast<std::string>(i+1) + “,”;
strTemp += boost::lexical_cast<std::string>(i+2) + “);”;
std::string strSql(“INSERT INTO exam_en(language,math,computer) VALUES “ + strTemp );
postgres->insert( (char)strSql.c_str() );
}
char sql[] = “SELECT * FROM exam_en;”;
res = postgres->fetch(sql);
map_result::iterator it = res.begin();
for( ; it!=res.end(); ++it )
{
std::cout << “ROW:” << it->first << std::endl;
map<string,string>::iterator itField = it->second.begin();
for( ; itField!=it->second.end(); ++itField )
{
std::cout << “Field:” << itField->first << “ Value:” << itField->second << std::endl;
}
}
return 0;
}
