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From: Oliver Fischer <nexus@fileseeker.net>
To: pgsql-interfaces@postgresql.org
Subject: PQclear() causes coredump
Date: Sun, 15 Oct 2000 20:19:17 +0200
Message-ID: <005501c036d4$6e37c810$0fed54d4@leveld.de> (raw)

Hi Folks,

I write a program in c++ using PostgreSQL 7.0 at the moment.
During this, I have
written some small classes for accessing the database. One of
this classes is QtResultSet. I use them to manage my statments.

To avoid memory leaks, I use the dtor to free the resultset with
PQclear(). Unfortunaly every call to PQclear causes a coredump.
What is my mistake?

=== QtResultSet.h ===

#include <string>
#include <map>
#include <vector>
#include <libpq-fe.h>
#include "../errors/QtExceptions.h"

#ifndef __QTRESULTSET__
#define __QTRESULTSET__

namespace qt {
  namespace database {
    using namespace std;
    using namespace qt::errors;

    class QtResultSet {
    public:

      virtual ~QtResultSet();

      vector<string> fieldnames() throw(QtDbConnectionBadErr,
QtDbFatalErr,
     QtDbNonfatalErr, QtDbBadResponseErr);
      vector<string> fetch(int) throw(QtDbConnectionBadErr,
QtDbFatalErr,
          QtDbNonfatalErr, QtDbBadResponseErr);
      vector<string> fetch(void) throw(QtDbConnectionBadErr,
QtDbFatalErr,
           QtDbNonfatalErr, QtDbBadResponseErr);

      string get_error();

      int rows();
      int fields();

      void execute() throw(QtDbConnectionBadErr, QtDbFatalErr,
      QtDbNonfatalErr, QtDbBadResponseErr);

      friend class QtConnection;


    protected:
      QtResultSet(PGconn *, const string &);

    private:
      void fetch_row(int, vector<string>*);
      bool binarydata_m;
      int rows_m;
      int fields_m;
      int currentrow_m;
      string query_m;
      string error_m;
      PGresult *pgresult_mp;
      PGconn *pgconn_mp;
    };

  } }
#endif

=== QtResultSet.cpp ===

#include <string>
#include <libpq-fe.h>
#include "QtResultSet.h"
#include "../errors/QtExceptions.h"

namespace qt {
  namespace database {
    using namespace std;
    using namespace qt::errors;

    QtResultSet::~QtResultSet() {

      PQclear(this->pgresult_mp);

    }

    QtResultSet::QtResultSet(PGconn *pgconn, const string &query)
{
      pgconn_mp    = pgconn;
      query_m      = query;
      fields_m     = 0;
      rows_m       = 0;
      currentrow_m = 0;
    }

    void QtResultSet::execute() throw(QtDbConnectionBadErr,
QtDbFatalErr,
          QtDbNonfatalErr, QtDbBadResponseErr)

      try {
 pgresult_mp = PQexec(pgconn_mp, query_m.c_str());

 ExecStatusType res = PQresultStatus(pgresult_mp);


 if (res == (PGRES_COMMAND_OK || PGRES_TUPLES_OK)) {
   rows_m       = PQntuples(pgresult_mp);
   fields_m     = PQnfields(pgresult_mp);
   binarydata_m = PQbinaryTuples(pgresult_mp);
   currentrow_m = -1;
 }
 else {
   error_m = PQresultErrorMessage(pgresult_mp);

   switch (res) {
     case PGRES_EMPTY_QUERY:
     break;

     case PGRES_BAD_RESPONSE:
     throw QtDbBadResponseErr();
     break;

     case PGRES_NONFATAL_ERROR:
     throw QtDbNonfatalErr();
     break;

     case PGRES_FATAL_ERROR:
     throw QtDbFatalErr();
     break;
   }
}
      }
      catch (...) {
#ifdef QTDEBUG
 cerr << "Exception catched and PQclear() called." << endl;
#endif QTDEBUG

 PQclear(pgresult_mp);

#ifdef QTDEBUG
 cerr << "Exception rethrown." << endl;
#endif QTDEBUG

 throw;
      }    }
    int QtResultSet::fields() {
      return fields_m;
    }
    int QtResultSet::rows() {
      return rows_m;
    }

        vector<string> QtResultSet::fieldnames()
throw(QtDbConnectionBadErr, QtDbFatalErr,
         QtDbNonfatalErr, QtDbBadResponseErr) {
      vector<string> row;

            for (int i = 0; i < rows_m; i++) {
 row.push_back(PQfname(pgresult_mp, i));
      }

      return row;
    }
    vector<string> QtResultSet::fetch(void)
throw(QtDbConnectionBadErr, QtDbFatalErr,
        QtDbNonfatalErr, QtDbBadResponseErr) {
      vector<string> row;

      if (currentrow_m < (rows_m - 1)) {
 this->fetch_row(++currentrow_m, &row);
      }
      else {
       }

      return row;
    }
    vector<string> QtResultSet::fetch(int id)
throw(QtDbConnectionBadErr, QtDbFatalErr,
          QtDbNonfatalErr, QtDbBadResponseErr) {
      vector<string> row;

      if ((id >  0)  && (id < rows_m)) {
 this->fetch_row(id, &row);
      }
      else {
      }

      return row;
    }
    void QtResultSet::fetch_row(int rowid, vector<string>
*rowdata) {

      for (int i = 0; i < fields_m; i++) {
 rowdata->push_back(string("Aber Hallo"));
      }

    }
    string QtResultSet::get_error() {
      return this->error_m;
    } // QtResultSet::get_error

  } // namespace database
}  // namespace qt


BYe,

Oliver
--
Oliver Fischer
Level of Detail, Brunnenstr. 196, D-10119 Berlin
Tel. +49/30/280 491 43

--
Oliver Fischer
Level of Detail, Brunnenstr. 196, D-10119 Berlin
Tel. +49/30/280 491 43

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  To: pgsql-interfaces@postgresql.org
  Cc: nexus@fileseeker.net
  Subject: Re: PQclear() causes coredump
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