SQL query C++ code (My first C++ application)

Question

I would really welcome some advice, and notes about my code. I am a long time Python user, and some days ago i decided i should try C++. So a couple of days passed, and i wrote my first application which has a practical use. I still find C++ very complicated (my current perspective is over complicated) but i can clearly say it is faster then my same python implementation.

The code:

/* 
 * File:   main.cpp
 * Author: gerdos
 *
 * Created on October 10, 2016, 4:23 PM
 */

#include <string>
#include <iostream>
#include <unistd.h>
#include <list>
#include <vector>
#include <algorithm>

#include <mysql_connection.h>
#include <cppconn/driver.h>
#include <cppconn/exception.h>
#include <cppconn/resultset.h>
#include <cppconn/statement.h>
#include <cppconn/resultset_metadata.h>

using namespace sql;
using namespace std;

int main(int argc, char* argv[]){
    int opt;
    vector<string> column_name_list;

    // Shut GetOpt error messages down (return '?'): 
    opterr = 0;

    // Retrieve the options:
    while ( (opt = getopt(argc, argv, "F:")) != -1 ) {  // for each option...
        if (opt == 'F'){
            column_name_list.insert(column_name_list.end(), string(optarg));       
        }
    }
    string queries;
    for (unsigned i = 1; i < argc; i++){
        if (string(argv[i]) != "-F" && find(column_name_list.begin(), column_name_list.end(), argv[i]) == column_name_list.end()){
            queries += "'" + string(argv[i]) + "',";
        }
    }

    string columns;
    for (unsigned i = 0; i < column_name_list.size(); i++){
        columns += column_name_list[i] + ",";
    }
    columns.erase(columns.size()-1);
    queries.erase(queries.size()-1);

    try{
        sql::Driver *driver;
        sql::Connection *con;
        sql::Statement *stmt;
        sql::ResultSet *res;

        driver = get_driver_instance();

        con = driver->connect("sql_adress", "user", "nope"); // Join a server
        con->setSchema("database_name"); // Use a database

        stmt = con->createStatement();
        res = stmt->executeQuery(string("select " + columns + " from table_name where accession in (" + queries + ")"));

        sql::ResultSetMetaData *res_meta = res -> getMetaData();
        int cols = res_meta -> getColumnCount();
        if (res->rowsCount() == 0){
            cout << "Query not found!" << endl;
            return 0;
        }
        while (res->next()) {
            for (unsigned i = 1; i <= cols; i++){
                cout << res->getString(i) << endl;
            }  
        }
        delete res;
        delete stmt;
        delete con;
    }  
    // No idea about this part yet, copied it from a tutorial
    catch (sql::SQLException &e){
        cout << "# ERR: SQLException in " << __FILE__;
        cout << "(" << __FUNCTION__ << ") on line " << __LINE__ << endl;
        cout << "# ERR: " << e.what();
        cout << " (MySQL error code: " << e.getErrorCode();
        cout << ", SQLState: " << e.getSQLState() << " )" << endl;
    }
    return 0;
}

Answer 1

I found this code very difficult to understand, and I feel that I won't be alone. I can't refactor it (for the aforementioned reason) nevertheless some advice which you might find instructive:

• Please use names which people will make sense of: column_name_list, opt, "F", opterr etc etc - this makes reading code very difficult.
• formatting - please use good formatting it all makes a difference.
• break things up into methods so that each method is doing only one thing.
• Add better comments if things are not self-explanatory.

My two cents.