I am learning to write C++ code to access data in a MySQL database. My goal is to use a separate class to control the database access so I can use this class elsewhere. To facilitate my learning, I'm working on simple code to connect to a database (success!) and return all rows in a simple and small table (failing!).

The connection is OK through the class constructor but I'm getting a segmentation fault in the queryResults = query.store() in the class method. The backtrace, as I read it, says the failure is in a MySQL routine. (PS: The gtkmm.h is because I eventually want this class to be used by a GUI written in gtkmm.)

Any suggestions would be greatly appreciated!


[program messages and backtrace of gdb:]
Starting program: /home/dave/Code/mysql/main 
[Thread debugging using libthread_db enabled]
main: Trying to instantiate db class...
database: Trying to connect to test...
database: Connection was successful.
main: After instantiation of db class
main: Calling dbselect using:SELECT * FROM SourceType ORDER BY SourceTypeId
database: Do query using SELECT * FROM SourceType ORDER BY SourceTypeId
database: Did 'query << selectsql' 

Program received signal SIGSEGV, Segmentation fault.
0x00f15e94 in mysql_send_query () from /usr/lib/libmysqlclient.so.16
(gdb) bt
#0  0x00f15e94 in mysql_send_query () from /usr/lib/libmysqlclient.so.16
#1  0x00f15f30 in mysql_real_query () from /usr/lib/libmysqlclient.so.16
#2  0x00e8445f in mysqlpp::Query::store(char const*, unsigned int) ()
   from /usr/lib/libmysqlpp.so.3
#3  0x00e86e05 in mysqlpp::Query::store(mysqlpp::SQLTypeAdapter const&) ()
   from /usr/lib/libmysqlpp.so.3
#4  0x0804b2ae in mysqlpp::Query::store (this=0xbffff250)
    at /usr/include/mysql++/query.h:467
#5  0x0804a9b7 in DataBase::dbselect (this=0xbffff238, selectsql=...)
    at database.cc:31
#6  0x0804c74f in main ()
[end backtrace]

my main C++ code

#include <gtkmm.h>
#include <iostream>
#include <mysql++.h>
#include <stdlib.h>
#include "database.h"

using namespace std;
using namespace mysqlpp;

int main() {

Glib::ustring SQLstring;
size_t rows = 0;
StoreQueryResult results;

  cout << "main: Trying to instantiate db class...\n";
    DataBase wwdb("test");
    cout << "main: After instantiation of db class\n";

    SQLstring = "SELECT * FROM SourceType ORDER BY SourceTypeId";   
  cout << "main: Calling dbselect using:" << SQLstring <<"\n";
    if (wwdb.dbselect(SQLstring)) {
        cout << "main: Successful!";
        rows = wwdb.returnRows();
        results = wwdb.returnResults();
      cout << "Rows=" << rows << "\n";
        for (size_t i = 0; i < rows; i++)
            cout << "main: ID: " << results[i]["SourceTypeId"] << " - Name: " << results[i]["SourceTypeName"] << endl;
        cout << "main: Select done.\n";
    else {
        cout << "main: FAILED\n";
        return -1;

my class header:

#ifndef DATABASE_H
#define DATABASE_H

#include <gtkmm.h>
#include <stdlib.h>
#include <mysql++.h>

using namespace std;
using namespace mysqlpp;

class DataBase
  DataBase(Glib::ustring db);
  virtual ~DataBase();

    bool dbselect(const Glib::ustring&);
    size_t returnRows();
    StoreQueryResult returnResults();
    bool dbinsert(Glib::ustring&);

    Connection conn; 
    Query query; 
    StoreQueryResult queryResults;
    size_t rows;

#endif //DATABASE_H

my database class methods:

#include <iostream>
#include <mysql++.h>
#include <stdlib.h>
#include <string>
#include "database.h"

using namespace std;
using namespace mysqlpp;

//Constructor - Connect to DB
DataBase::DataBase(Glib::ustring db) : query(&conn, true) {
    cout << "database: Trying to connect to " << db <<"...\n";
    conn = new Connection("wwindextest", "localhost", "guest");
    if (!conn) {
        cout << "FAILED due to: " << conn.error() << "\n";
    cout << "database: Connection was successful.\n";
    query = conn.query();

//Destructor - disconnect from DB
DataBase::~DataBase() {

bool DataBase::dbselect(const Glib::ustring& selectsql) {
    cout << "database: Do query using " << selectsql << "\n";
    query << selectsql;
    cout << "database: Did 'query << selectsql' \n";
    if (queryResults = query.store()) {
        cout << "Successful!  Rows=";
        rows = queryResults.num_rows();
        cout << rows << "\n";
        return true;
    else {
        cout << "FAILED due to " << query.error() << "\n";
        return false;

size_t DataBase::returnRows() {
    return rows;

StoreQueryResult DataBase::returnResults() {
    return queryResults;

bool DataBase::dbinsert(Glib::ustring& insertsql)
    cout << "Do Insert here\n";
    return true;
/* To insert stuff with escaping */
/*cout << "Trying to insert...\n";
query << "INSERT INTO table " <<
"VALUES (" <<
"\"" << escape << insertData << "\"" <<
cout << "insert done.\n";

    return 0;

Edited by mike_2000_17: Fixed formatting

6 Years
Discussion Span
Last Post by DAlexNagy

The problem is an incompatibility between the GTK programs and MySQL++. I have moved to using GDA and this is working!

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