Initializing a static std::map<int, int> in C++

Question

What is the right way of initializing a static map? Do we need a static function that will initialize it?

Answer 1

Using Boost.Assign:

#include <map>
#include "boost/assign.hpp"
using namespace std;
using namespace boost::assign;


map<int, int> m = map_list_of (1,2) (3,4) (5,6) (7,8);

Answer 2

I would wrap the map inside a static object, and put the map initialisation code in the constructor of this object, this way you are sure the map is created before the initialisation code is executed.

Answer 3

Best way is to use a function:

#include <map>

using namespace std;

map<int,int> create_map()
{
  map<int,int> m;
  m[1] = 2;
  m[3] = 4;
  m[5] = 6;
  return m;
}

map<int,int> m = create_map();

Answer 4

This is similar to PierreBdR, without copying the map.

#include <map>

using namespace std;

bool create_map(map<int,int> &m)
{
  m[1] = 2;
  m[3] = 4;
  m[5] = 6;
  return true;
}

static map<int,int> m;
static bool _dummy = create_map (m);

Answer 5

Here is another way that uses the 2-element data constructor. No functions are needed to initialize it.

#include <map>
#include <string>

typedef std::map<std::string, int> MyMap;

const MyMap::value_type rawData[] = {
   MyMap::value_type("hello", 42),
   MyMap::value_type("world", 88),
};
const int numElems = sizeof rawData / sizeof rawData[0];
MyMap myMap(rawData, rawData + numElems);