PostgreSQL简单封装

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 <st<a href="https://www.jb51.cc/tag/dio/" target="_blank" class="keywords">dio</a>.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 *<a href="https://www.jb51.cc/tag/sql/" target="_blank" class="keywords">sql</a>); int insert(char *<a href="https://www.jb51.cc/tag/sql/" target="_blank" class="keywords">sql</a>); 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,"<a href="https://www.jb51.cc/tag/Could/" target="_blank" class="keywords">Could</a> not connect to db/n<a href="https://www.jb51.cc/tag/s/" target="_blank" class="keywords">%s</a>",PQerrorMessage(conn)); finish_connection(conn); } } Conn::~Conn() { finish_connection(conn); } void Conn::reset() { PQfinish(conn); conn = PQconnectdb(conninfo); } map_result Conn::fetch(char *<a href="https://www.jb51.cc/tag/sql/" target="_blank" class="keywords">sql</a>) { int row,col; map_result results; map<string,string> pa<a href="https://www.jb51.cc/tag/irs/" target="_blank" class="keywords">irs</a>; // 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,"<a href="https://www.jb51.cc/tag/Failed/" target="_blank" class="keywords">Failed</a> to BEGIN transaction /n<a href="https://www.jb51.cc/tag/s/" target="_blank" class="keywords">%s</a>",PQerrorMessage(conn)); PQclear(res); finish_connection(conn); } // Set up fetch query with a CURSOR: string Final<a href="https://www.jb51.cc/tag/sql/" target="_blank" class="keywords">sql</a> = string("DECLARE myportal CURSOR FOR ") + string(<a href="https://www.jb51.cc/tag/sql/" target="_blank" class="keywords">sql</a>); // Declare CURSOR and execute query: res = PQexec(conn,Final<a href="https://www.jb51.cc/tag/sql/" target="_blank" class="keywords">sql</a>.c_<a href="https://www.jb51.cc/tag/str/" target="_blank" class="keywords">str()</a>); if (PQresultStatus(res) != PGRES_COMMAND_OK) { fprintf(stderr,"QUERY <a href="https://www.jb51.cc/tag/Failed/" target="_blank" class="keywords">Failed</a>/n<a href="https://www.jb51.cc/tag/s/" target="_blank" class="keywords">%s</a>/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 <a href="https://www.jb51.cc/tag/Failed/" target="_blank" class="keywords">Failed</a>/n<a href="https://www.jb51.cc/tag/s/" target="_blank" class="keywords">%s</a>/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); co<a href="https://www.jb51.cc/tag/L/" target="_blank" class="keywords">L++</a>) { pa<a href="https://www.jb51.cc/tag/irs/" target="_blank" class="keywords">irs</a>[PQfname(res,col)] = PQgetvalue(res,row,col); } results[row] = pa<a href="https://www.jb51.cc/tag/irs/" target="_blank" class="keywords">irs</a>; } } return results; } int Conn::insert(char *<a href="https://www.jb51.cc/tag/sql/" target="_blank" class="keywords">sql</a>) { // 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,"<a href="https://www.jb51.cc/tag/Failed/" target="_blank" class="keywords">Failed</a> to BEGIN transaction /n<a href="https://www.jb51.cc/tag/s/" target="_blank" class="keywords">%s</a>/n",PQerrorMessage(conn)); PQclear(res); finish_connection(conn); } // Execute Insert: res = PQexec(conn,<a href="https://www.jb51.cc/tag/sql/" target="_blank" class="keywords">sql</a>); if (PQresultStatus(res) != PGRES_COMMAND_OK) { fprintf(stderr,"<a href="https://www.jb51.cc/tag/Failed/" target="_blank" class="keywords">Failed</a> to execute INSERT /n<a href="https://www.jb51.cc/tag/s/" target="_blank" class="keywords">%s</a>/n",PQerrorMessage(conn)); PQclear(res); finish_connection(conn); } // COMMIT transaction: res = PQexec(conn,"COMMIT"); if (PQresultStatus(res) != PGRES_COMMAND_OK) { fprintf(stderr,"<a href="https://www.jb51.cc/tag/Failed/" target="_blank" class="keywords">Failed</a> to COMMIT transaction/n<a href="https://www.jb51.cc/tag/s/" target="_blank" class="keywords">%s</a>/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("<a href="https://www.jb51.cc/tag/dbn/" target="_blank" class="keywords">dbn</a>ame=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 str<a href="https://www.jb51.cc/tag/sql/" target="_blank" class="keywords">sql</a>("INSERT INTO exam_en(language,math,co<a href="https://www.jb51.cc/tag/mpu/" target="_blank" class="keywords">mpu</a>ter) VALUES " + strTemp ); postgres->insert( (char*)str<a href="https://www.jb51.cc/tag/sql/" target="_blank" class="keywords">sql</a>.c_<a href="https://www.jb51.cc/tag/str/" target="_blank" class="keywords">str()</a> ); } char <a href="https://www.jb51.cc/tag/sql/" target="_blank" class="keywords">sql</a>[] = "SELECT * FROM exam_en;"; res = postgres->fetch(<a href="https://www.jb51.cc/tag/sql/" target="_blank" class="keywords">sql</a>); map_result::i<a href="https://www.jb51.cc/tag/tera/" target="_blank" class="keywords">tera</a>tor it = res.begin(); for( ; it!=res.end(); ++it ) { std::cout << "ROW:" << it->f<a href="https://www.jb51.cc/tag/irs/" target="_blank" class="keywords">irs</a>t << std::endl; map<string,string>::i<a href="https://www.jb51.cc/tag/tera/" target="_blank" class="keywords">tera</a>tor itField = it->second.begin(); for( ; itField!=it->second.end(); ++itField ) { std::cout << "Field:" << itField->f<a href="https://www.jb51.cc/tag/irs/" target="_blank" class="keywords">irs</a>t << " Value:" << itField->second << std::endl; } } return 0; }

原文地址：https://www.jb51.cc/postgresql/196997.html