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Description

The C++ constructor std::map::map() constructs a map with as many elements as in range of first to last.

Declaration

Following is the declaration for std::map::map() constructor form std::map header.

C++98

template <class InputIterator>
map (InputIterator first, InputIterator last,
     const key_compare& comp = key_compare(),
     const allocator_type& alloc = allocator_type());

C++11

template <class InputIterator>
map (InputIterator first, InputIterator last,
     const key_compare& comp = key_compare(),
     const allocator_type& = allocator_type());

Parameters

• first − Input iterator to initial position.

• last − Input iterator to final position.

• comp − A binary predicate, which takes two key arguments and returns true if first argument goes before second otherwise false. By default it uses less<key_type> predicate.

• alloc − The allocator object.

Return value

Constructor never returns value.

Exceptions

This member function never throws exception.

Time complexity

Linear i.e. O(n)

Example

The following example shows the usage of std::map::map() constructor.

#include <iostream>
#include <map>

using namespace std;

int main(void) {
   map<char, int> m1 = {
            {'a', 1},
            {'b', 2},
            {'c', 3},
            {'d', 4},
            {'e', 5}
            };

   map<char, int> m2(m1.begin(), m1.end());

   cout << "Map contains following elements" << endl;

   for (auto it = m2.begin(); it != m2.end(); ++it)
      cout << it->first << " = " << it->second << endl;

   return 0;
}

Let us compile and run the above program, this will produce the following result −

Map contains following elements
a = 1
b = 2
c = 3
d = 4
e = 5

map.htm