GeezerVison

The World Wide Web, restored to 800 pixels of glory.

Home|About|Gaming cabinet|Archives|How it works|Starter sites

GeezerVison is showing cplusplus.com — std::unordered_map::hash_function

C++

Reference

C library:
- <cassert> (assert.h)
- <cctype> (ctype.h)
- <cerrno> (errno.h)
- C++11
  <cfenv> (fenv.h)
- <cfloat> (float.h)
- C++11
  <cinttypes> (inttypes.h)
- <ciso646> (iso646.h)
- <climits> (limits.h)
- <clocale> (locale.h)
- <cmath> (math.h)
- <csetjmp> (setjmp.h)
- <csignal> (signal.h)
- <cstdarg> (stdarg.h)
- C++11
  <cstdbool> (stdbool.h)
- <cstddef> (stddef.h)
- C++11
  <cstdint> (stdint.h)
- <cstdio> (stdio.h)
- <cstdlib> (stdlib.h)
- <cstring> (string.h)
- C++11
  <ctgmath> (tgmath.h)
- <ctime> (time.h)
- C++11
  <cuchar> (uchar.h)
- <cwchar> (wchar.h)
- <cwctype> (wctype.h)
Containers:
- C++11
  <array>
- <deque>
- C++11
  <forward_list>
- <list>
- <map>
- <queue>
- <set>
- <stack>
- C++11
  <unordered_map>
- C++11
  <unordered_set>
- <vector>
Input/Output:
- <fstream>
- <iomanip>
- <ios>
- <iosfwd>
- <iostream>
- <istream>
- <ostream>
- <sstream>
- <streambuf>
Multi-threading:
- C++11
  <atomic>
- C++11
  <condition_variable>
- C++11
  <future>
- C++11
  <mutex>
- C++11
  <thread>
Other:
- <algorithm>
- <bitset>
- C++11
  <chrono>
- C++11
  <codecvt>
- <complex>
- <exception>
- <functional>
- C++11
  <initializer_list>
- <iterator>
- <limits>
- <locale>
- <memory>
- <new>
- <numeric>
- C++11
  <random>
- C++11
  <ratio>
- C++11
  <regex>
- <stdexcept>
- <string>
- C++11
  <system_error>
- C++11
  <tuple>
- C++11
  <type_traits>
- C++11
  <typeindex>
- <typeinfo>
- <utility>
- <valarray>

<unordered_map>

C++11
unordered_map
C++11
unordered_multimap

unordered_map

C++11
unordered_map::~unordered_map
C++11
unordered_map::unordered_map
member functions
- C++11
  unordered_map::at
- C++11
  unordered_map::begin
- C++11
  unordered_map::bucket
- C++11
  unordered_map::bucket_count
- C++11
  unordered_map::bucket_size
- C++11
  unordered_map::cbegin
- C++11
  unordered_map::cend
- C++11
  unordered_map::clear
- C++11
  unordered_map::count
- C++11
  unordered_map::emplace
- C++11
  unordered_map::emplace_hint
- C++11
  unordered_map::empty
- C++11
  unordered_map::end
- C++11
  unordered_map::equal_range
- C++11
  unordered_map::erase
- C++11
  unordered_map::find
- C++11
  unordered_map::get_allocator
- C++11
  unordered_map::hash_function
- C++11
  unordered_map::insert
- C++11
  unordered_map::key_eq
- C++11
  unordered_map::load_factor
- C++11
  unordered_map::max_bucket_count
- C++11
  unordered_map::max_load_factor
- C++11
  unordered_map::max_size
- C++11
  unordered_map::operator[]
- C++11
  unordered_map::operator=
- C++11
  unordered_map::rehash
- C++11
  unordered_map::reserve
- C++11
  unordered_map::size
- C++11
  unordered_map::swap
non-member overloads
- C++11
  operators (unordered_map)
- C++11
  swap (unordered_map)

public member type

<unordered_map>

std::unordered_map::hash_function

hasher hash_function() const;

Get hash function

Returns the hash function object used by the unordered_map container.

The hash function is a unary function that takes an object of type key_type as argument and returns a unique value of type size_t based on it. It is adopted by the container on construction (see unordered_map's constructor for more info). By default, it is the default hashing function for the corresponding key type: hash<key_type>.

Parameters

none

Return Value

The hash function.

Member type hasher is the type of the hash function used by the container, defined in unordered_map as an alias of its third template parameter (Hash).

Example

// unordered_map::hash_function
#include <iostream>
#include <string>
#include <unordered_map>

typedef std::unordered_map<std::string,std::string> stringmap;

int main ()
{
  stringmap mymap;

  stringmap::hasher fn = mymap.hash_function();

  std::cout << "this: " << fn ("this") << std::endl;
  std::cout << "thin: " << fn ("thin") << std::endl;

  return 0;
}

Possible output:

this: 671344778
thin: 3223852919

Notice how two similar strings yield quite different hash values.

Complexity

Constant.

Iterator validity

No changes.

See also

unordered_map::key_eq: Get key equivalence predicate (public member type)

unordered_map::get_allocator: Get allocator (public member function)

Home page | Privacy policy
© cplusplus.com, 2000-2026 - All rights reserved - v3.3.4s
Spotted an error? contact us

You are visitor 01402503 — GeezerVison does not store the pages you look up.
Best viewed with Netscape Navigator 4.7 or Internet Explorer 6 at 800×600. No cookies required.