unordered_map::load_factor

Counts the average elements per bucket.

float load_factor() const;

Remarks

The member function returns (float)unordered_map::size() / (float)unordered_map::bucket_count(), the average number of elements per bucket.

Example

// std_tr1__unordered_map__unordered_map_load_factor.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; 
 
// inspect current parameters 
    std::cout << "bucket_count() == " << c1.bucket_count() << std::endl; 
    std::cout << "load_factor() == " << c1.load_factor() << std::endl; 
    std::cout << "max_bucket_count() == " 
        << c1.max_bucket_count() << std::endl; 
    std::cout << "max_load_factor() == " 
        << c1.max_load_factor() << std::endl; 
    std::cout << std::endl; 
 
// change max_load_factor and redisplay 
    c1.max_load_factor(0.10f); 
    std::cout << "bucket_count() == " << c1.bucket_count() << std::endl; 
    std::cout << "load_factor() == " << c1.load_factor() << std::endl; 
    std::cout << "max_bucket_count() == " 
        << c1.max_bucket_count() << std::endl; 
    std::cout << "max_load_factor() == " 
        << c1.max_load_factor() << std::endl; 
    std::cout << std::endl; 
 
// rehash and redisplay 
    c1.rehash(100); 
    std::cout << "bucket_count() == " << c1.bucket_count() << std::endl; 
    std::cout << "load_factor() == " << c1.load_factor() << std::endl; 
    std::cout << "max_bucket_count() == " 
        << c1.max_bucket_count() << std::endl; 
    std::cout << "max_load_factor() == " 
        << c1.max_load_factor() << std::endl; 
    std::cout << std::endl; 
 
    return (0); 
    } 
 

 [c, 3] [b, 2] [a, 1]
bucket_count() == 8
load_factor() == 0.375
max_bucket_count() == 8
max_load_factor() == 4

bucket_count() == 8
load_factor() == 0.375
max_bucket_count() == 8
max_load_factor() == 0.1

bucket_count() == 128
load_factor() == 0.0234375
max_bucket_count() == 128
max_load_factor() == 0.1

Requirements

Header: <unordered_map>

Namespace: std

See Also

Reference

<unordered_map>

unordered_map Class

unordered_map::bucket_count

unordered_map::max_load_factor

Other Resources

<unordered_map> Members