unordered_map::rehash
Rebuilds the hash table.
void rehash(size_type nbuckets);
Parameters
- nbuckets
The requested number of buckets.
Remarks
The member function alters the number of buckets to be at least nbuckets and rebuilds the hash table as needed.
Example
// std_tr1__unordered_map__unordered_map_rehash.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_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_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_load_factor() == " << c1.max_load_factor() << std::endl;
return (0);
}
[c, 3] [b, 2] [a, 1] bucket_count() == 8 load_factor() == 0.375 max_load_factor() == 4 bucket_count() == 8 load_factor() == 0.375 max_load_factor() == 0.1 bucket_count() == 128 load_factor() == 0.0234375 max_load_factor() == 0.1
Requirements
Header: <unordered_map>
Namespace: std