unordered_map::unordered_map

Constructs a container object.

unordered_map(
    const unordered_map& right);
explicit unordered_map(
    size_type nbuckets = N0,
    const Hash& hfn = Hash(),
    const Pred& comp = Pred(),
    const Alloc& al = Alloc());
template<class InIt>
    unordered_map(
    InIt first, InIt last,
    size_type nbuckets = N0,
    const Hash& hfn = Hash(),
    const Pred& comp = Pred(),
    const Alloc& al = Alloc());
unordered_map(
    unordered_map&& right);

Parameters

Remarks

The first constructor specifies a copy of the sequence controlled by right. The second constructor specifies an empty controlled sequence. The third constructor inserts the sequence of element values [first, last). The fourth constructor specifies a copy of the sequence by moving right.

All constructors also initialize several stored values. For the copy constructor, the values are obtained from right. Otherwise:

the minimum number of buckets is the argument nbuckets, if present; otherwise it is a default value described here as the implementation-defined value N0.

the hash function object is the argument hfn, if present; otherwise it is Hash().

the comparison function object is the argument comp, if present; otherwise it is Pred().

the allocator object is the argument al, if present; otherwise, it is Alloc().

Example

// std__unordered_map__unordered_map_construct.cpp 
// compile with: /EHsc 
#include <unordered_map> 
#include <iostream> 

typedef std::unordered_map<char, int> Mymap; 
int main() 
    { 
    Mymap c1; 
 
    c1.insert(Mymap::value_type('a', 1)); 
    c1.insert(Mymap::value_type('b', 2)); 
    c1.insert(Mymap::value_type('c', 3)); 
 
// display contents " [c 3] [b 2] [a 1]" 
    for (Mymap::const_iterator it = c1.begin(); 
        it != c1.end(); ++it) 
        std::cout << " [" << it->first << ", " << it->second << "]"; 
    std::cout << std::endl; 
 
    Mymap c2(8, 
        std::tr1::hash<char>(), 
        std::equal_to<char>(), 
        std::allocator<std::pair<const char, int> >()); 
 
    c2.insert(Mymap::value_type('d', 4)); 
    c2.insert(Mymap::value_type('e', 5)); 
    c2.insert(Mymap::value_type('f', 6)); 
 
// display contents " [f 6] [e 5] [d 4]" 
    for (Mymap::const_iterator it = c2.begin(); 
        it != c2.end(); ++it) 
        std::cout << " [" << it->first << ", " << it->second << "]"; 
    std::cout << std::endl; 
 
    Mymap c3(c1.begin(), 
        c1.end(), 
        8, 
        std::tr1::hash<char>(), 
        std::equal_to<char>(), 
        std::allocator<std::pair<const char, int> >()); 
 
// display contents " [c 3] [b 2] [a 1]" 
    for (Mymap::const_iterator it = c3.begin(); 
        it != c3.end(); ++it) 
        std::cout << " [" << it->first << ", " << it->second << "]"; 
    std::cout << std::endl; 

    Mymap c4(std::move(c3));

// display contents " [c 3] [b 2] [a 1]" 
    for (Mymap::const_iterator it = c4.begin(); 
        it != c4.end(); ++it) 
        std::cout << " [" << it->first << ", " << it->second << "]"; 
    std::cout << std::endl; 
 
    return (0); 
    } 
 

 [c, 3] [b, 2] [a, 1]
 [f, 6] [e, 5] [d, 4]
 [c, 3] [b, 2] [a, 1]
 [c, 3] [b, 2] [a, 1]

Requirements

Header: <unordered_map>

Namespace: std

See Also

Reference

<unordered_map>

unordered_map Class

Other Resources

<unordered_map> Members