Question

I am trying to copy a database table in a map where its the primary key will be the key of map and the rest of the columns are instances of boost:vector. I am new to boost as well as variadic templates. I have tried to write a wrapper, but it works fine only for a fixed number of columns. Following is the code

#include <boost/container/vector.hpp>
#include <iostream>
#include <string>
#include <map>
#include <type_traits>

typedef boost::container::vector<std::string> MAPPED_COLS;
typedef std::map <int,  MAPPED_COLS >    TABLE ;
typedef std::map <int,  MAPPED_COLS > ::iterator ROW_ITER;

typedef std::string  str;

template <typename str>
class MappedTable
{
    private:
            TABLE           mapTable;
            MAPPED_COLS     cols;
            ROW_ITER        row;

            std::string     scTableName;
            int             iRows;
            int             iCols;
    public:
            MappedTable()  { iCols=3; }

            MappedTable(int iNumCols)  { iCols=iNumCols;}
            ~MappedTable() { }

            template <str>
            void    fnRowCols()     //termination version
            {
            }

            template <str>
            void    fnCols(const str& scCol2, const str& scCol3,...)
            {
                    if(cols.size()>=iCols)
                    {
                          cols.erase (cols.begin(),cols.begin()+iCols);
                    }
                    cols.push_back(scCol2);

                    fnCols(scCol3,...);
            }

            template <str>
            void fnMapRow(int iCol1,const str& scCol2,...)
            {
                    fnCols(scCol2,...);
                    mapTable[iCol1]=MAPPED_COLS(cols);
            }


            MAPPED_COLS& fnGetRow(int iFindKey)
            {
                    row=mapTable.find(iFindKey);
                    if(row!=mapTable.end())
                            return (row->second);
            }
 };

Following is the main() for the above wrapper which works fine if i am not using variadic templates in my wrapper:-

 int main()
 {
    MappedTable Table(3) ;

    std::string vid[]={"11", "21", "51", "41"};
    std::string fare[]={"100", "400", "200", "4000"};
    std::string vehicle[]={"bus", "car", "train", "aeroplane"};

    int i=0;

    for(i=0;i<4;i++)
    {
            Table.fnMapRow(i,vid[i],fare[i],vehicle[i]);
    }

    for(i=0;i<4;i++)
    {
            MAPPED_COLS mpCol=Table.fnGetRow(i);
            std::cout<<"\n  "<<i<<" "<<mpCol[0]<<" "<<mpCol[1]<<" "<<mpCol[2];
    }

    std::cout<<"\n";

    return 0;
}

The code was compiled with Boost 1.51.0 and gcc 4.4 with std=c++0x option

Can anyone suggest me what is that i am missing?
I am open to better ideas and as well as keen to know how this particular example would work even if not efficient enough.

The working code snippet is available in my answer below (Thanks to Rost).
It would be great if anyone can suggest some better and more methods to store an entire table into a map.

Thanks !!

Answer 1

Your variadic template function syntax doesn’t look correct. It shall be like this:

 template <typename... VarArgs>
 void fnCols(const str& scCol2, const str& scCol3, const VarArgs&... args)
 {
     // Non-relevant code skipped
     fnCols(scCol3, args...); // Recursive call with expanding arguments pack
 } 

Similar problem with fnMapRow.
Also template <str> is not needed before template member function definitions.