map::map

Constructs a map that is empty or that is a copy of all or part of some other map.

map( );
explicit map(
    const Traits& Comp
);
map(
    const Traits& Comp,
    const Allocator& Al
);
map(
    const map& Right
); 
map(
    map&& Right
);
map(
    initializer_list<value_type> IList
);
map(
    initializer_list<value_type> IList,
    const Traits& Comp
);
map(
    initializer_list<value_type> IList,
    const Traits& Comp, 
    const Allocator& Allocator
);
template<class InputIterator>
    map(
        InputIterator First,
        InputIterator Last
    );
template<class InputIterator>
    map(
        InputIterator First,
        InputIterator Last,
        const Traits& Comp
    );
template<class InputIterator>
    map(
        InputIterator First,
        InputIterator Last,
        const Traits& Comp,
        const Allocator& Al
    );

Parameters

Remarks

All constructors store a type of allocator object that manages memory storage for the map and that can later be returned by calling get_allocator. The allocator parameter is often omitted in the class declarations and preprocessing macros used to substitute alternative allocators.

All constructors initialize their map.

All constructors store a function object of type Traits that is used to establish an order among the keys of the map and that can later be returned by calling key_comp.

The first three constructors specify an empty initial map, the second specifying the type of comparison function (Comp) to be used in establishing the order of the elements and the third explicitly specifying the allocator type (Al) to be used. The key word explicit suppresses certain kinds of automatic type conversion.

The fourth constructor specifies a copy of the map Right.

The fifth constructor specifies a copy of the map by moving Right.

The sixth, seventh, and eighth constructors use an initializer_list from which to copy the members.

The next three constructors copy the range [First, Last) of a map with increasing explicitness in specifying the type of comparison function of class Traits and allocator.

Example

// map_map.cpp
// compile with: /EHsc
#include <map>
#include <iostream>

int main()
{
    using namespace std;
    typedef pair <int, int> Int_Pair;
    map <int, int>::iterator m1_Iter, m3_Iter, m4_Iter, m5_Iter, m6_Iter, m7_Iter;
    map <int, int, less<int> >::iterator m2_Iter;

    // Create an empty map m0 of key type integer
    map <int, int> m0;

    // Create an empty map m1 with the key comparison
    // function of less than, then insert 4 elements
    map <int, int, less<int> > m1;
    m1.insert(Int_Pair(1, 10));
    m1.insert(Int_Pair(2, 20));
    m1.insert(Int_Pair(3, 30));
    m1.insert(Int_Pair(4, 40));

    // Create an empty map m2 with the key comparison
    // function of geater than, then insert 2 elements
    map <int, int, less<int> > m2;
    m2.insert(Int_Pair(1, 10));
    m2.insert(Int_Pair(2, 20));

    // Create a map m3 with the 
    // allocator of map m1
    map <int, int>::allocator_type m1_Alloc;
    m1_Alloc = m1.get_allocator();
    map <int, int> m3(less<int>(), m1_Alloc);
    m3.insert(Int_Pair(3, 30));

    // Create a copy, map m4, of map m1
    map <int, int> m4(m1);

    // Create a map m5 by copying the range m1[_First, _Last)
    map <int, int>::const_iterator m1_bcIter, m1_ecIter;
    m1_bcIter = m1.begin();
    m1_ecIter = m1.begin();
    m1_ecIter++;
    m1_ecIter++;
    map <int, int> m5(m1_bcIter, m1_ecIter);

    // Create a map m6 by copying the range m4[_First, _Last)
    // and with the allocator of map m2
    map <int, int>::allocator_type m2_Alloc;
    m2_Alloc = m2.get_allocator();
    map <int, int> m6(m4.begin(), ++m4.begin(), less<int>(), m2_Alloc);

    cout << "m1 =";
    for (auto i : m1)
        cout << i.first << " " << i.second << ", ";
    cout << endl;

    cout << "m2 =";
    for(auto i : m2)
        cout << i.first << " " << i.second << ", ";
    cout << endl;

    cout << "m3 =";
    for (auto i : m3)
        cout << i.first << " " << i.second << ", ";
    cout << endl;

    cout << "m4 =";
    for (auto i : m4)
        cout << i.first << " " << i.second << ", ";
    cout << endl;

    cout << "m5 =";
    for (auto i : m5)
        cout << i.first << " " << i.second << ", ";
    cout << endl;

    cout << "m6 =";
    for (auto i : m6)
        cout << i.first << " " << i.second << ", ";
    cout << endl;

    // Create a map m7 by moving m5
    cout << "m7 =";
    map<int, int> m7(move(m5));
    for (auto i : m7)
        cout << i.first << " " << i.second << ", ";
    cout << endl;

    // Create a map m8 by copying in an initializer_list
    map<int, int> m8{ { { 1, 1 }, { 2, 2 }, { 3, 3 }, { 4, 4 } } };
    cout << "m8: = ";
    for (auto i : m8)
        cout << i.first << " " << i.second << ", ";
    cout << endl;

    // Create a map m9 with an initializer_list and a comparator
    map<int, int> m9({ { 5, 5 }, { 6, 6 }, { 7, 7 }, { 8, 8 } }, less<int>());
    cout << "m9: = ";
    for (auto i : m9)
        cout << i.first << " " << i.second << ", ";
    cout << endl;

    // Create a map m10 with an initializer_list, a comparator, and an allocator
    map<int, int> m10({ { 9, 9 }, { 10, 10 }, { 11, 11 }, { 12, 12 } }, less<int>(), m9.get_allocator());
    cout << "m10: = ";
    for (auto i : m10)
        cout << i.first << " " << i.second << ", ";
    cout << endl;
}

Output

m1 = 10 20 30 40
m2 = 10 20
m3 = 30
m4 = 10 20 30 40
m5 = 10 20
m6 = 10
m7 = 10 20
m8: = 1 1, 2 2, 3 3, 4 4,
m9: = 5 5, 6 6, 7 7, 8 8,
m10: = 9 9, 10 10, 11 11, 12 12,

Requirements

Header: <map>

Namespace: std

See Also

Reference

map Class

Standard Template Library