Question

I am new in c++. I am trying to add a dragon object in cpp but i am receiving an error while adding the object

#include "dragon.h"
using std::cin;
#include <map>
using std::map;
#include <list>
#include <string>
#include <iostream>
using namespace std;
using std::list;

typedef map<string,list<Dragon> >::iterator iter;
typedef map<const string,list<Dragon> >::value_type dmaptype;
void display(map<string,list<Dragon> > dmap1,iter dmapiter1);


int main( )
{
  map<string,list<Dragon> >dmap;
iter dmapiter;

bool again = true;

string name;
double length;
string colour;
string location;
while( again )
{
     // get the details for the dragon
     cout << "\nEnter dragon name >> ";
     getline( cin, name );

     cout << "\nEnter dragon length >> ";
     cin >> length;

     cin.get( );

     cout << "\nEnter dragon colour >> ";
     getline( cin, colour );

     // now get the location
     cout << "\nEnter location >> ";
     getline( cin, location );
     dmapiter=dmap.find(location);

    Dragon * ptr ;
    ptr=new Dragon(name,length,colour);

     if(dmapiter==dmap.end())
     {
        list<Dragon*> dlist;
        dlist.push_back(ptr);
        dmap.insert(dmaptype(location, dlist));
     }
     else
     {
        dmapiter->second.push_back(*ptr);
     }
     char choice;

     cout << "\nEnter another dragon and location [ y / n ] ? ";
     cin >> choice;
     cin.get( );
     if( choice != 'y' && choice != 'Y' )
     {
          again = false;
     }

}
 display(dmap,dmapiter);


cout << endl;

return 0;


}

when i compile the program i am receiving an error at:

dmap.insert(dmaptype(location, dlist));

and the error is :

 error: no matching function for call to ‘std::pair<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::list<Dragon, std::allocator<Dragon> > >::pair(std::string&, std::list<Dragon*, std::allocator<Dragon*> >&)’
/usr/lib/gcc/i686-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/stl_pair.h:83: note: candidates are: std::pair<_T1, _T2>::pair(const _T1&, const _T2&) [with _T1 = const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, _T2 = std::list<Dragon, std::allocator<Dragon> >]
/usr/lib/gcc/i686-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/stl_pair.h:79: note:                 std::pair<_T1, _T2>::pair() [with _T1 = const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, _T2 = std::list<Dragon, std::allocator<Dragon> >]
/usr/lib/gcc/i686-redhat-linux/4.4.6/../../../../include/c++/4.4.6/bits/stl_pair.h:68: note:                 std::pair<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::list<Dragon, std::allocator<Dragon> > >::pair(const std::pair<const std::basic_string<char, std::char_traits<char>, std::allocator<char> >, std::list<Dragon, std::allocator<Dragon> > >&)

Any help will be appreciated…

Thank you

Answer 1

Try:

dmap.insert(std::make_pair(location, dlist));

but you also need to make the type of dlist consistent with that of your map – use list<Dragon> or list<Dragon*> for both.

For simplicity (so you don’t need to worry about deleting), try list<Dragon> first.
When you insert into this list, a copy will be made (since STL has value-semantics), so it’s ok if you create a Dragon locally on the stack to insert into dlist. (You can think of it as a copy being made: copy elision may occur if the compiler is smart, but don’t worry about that, for now).

For example:

Dragon dragon(name,length,colour);

if(dmapiter==dmap.end())
{
  list<Dragon> dlist;
  dlist.push_back(dragon);
  dmap.insert(make_pair(location, dlist));
}
else
{
  dmapiter->second.push_back(dragon);
}