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C++

Reference

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- C++11
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Containers:
- C++11
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  <forward_list>
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- C++11
  <unordered_map>
- C++11
  <unordered_set>
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  <atomic>
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<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)

function template

<unordered_map>

std::operators (unordered_map)

equality (1)

template <class Key, class T, class Hash, class Pred, class Alloc>  bool operator== ( const unordered_map<Key,T,Hash,Pred,Alloc>& lhs,                    const unordered_map<Key,T,Hash,Pred,Alloc>& rhs );

inequality (2)

template <class Key, class T, class Hash, class Pred, class Alloc>  bool operator!= ( const unordered_map<Key,T,Hash,Pred,Alloc>& lhs,                    const unordered_map<Key,T,Hash,Pred,Alloc>& rhs );

Relational operators for unordered_map

These overloaded global operator functions perform the appropriate equality or inequality comparison operation between the unordered_map containers lhs and rhs.

The procedure for the equality comparison is as follows (stopping at any point if the procedure finds a conclusive answer):

First, the sizes are compared.
Then, each key in one of the containers is looked for in the other, and if found, their values are compared.

Note that the unordered_map::hash_function and unordered_map::key_eq objects are expected to have the same behavior in both lhs and rhs.

Parameters

lhs, rhs: unordered_map containers (to the left- and right-hand side of the operator, respectively), having both the same template parameters (Key, T, Hash, Pred and Alloc).

Return Value

true if the condition holds, and false otherwise.

Example

// unordered_map comparisons
#include <iostream>
#include <string>
#include <unordered_map>

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

int main ()
{
  stringmap a = { {"AAPL","Apple"}, {"MSFT","Microsoft"}, {"GOOG","Google"} };
  stringmap b = { {"MSFT","Microsoft"}, {"GOOG","Google"}, {"AAPL","Apple"} };
  stringmap c = { {"MSFT","Microsoft Corp."}, {"GOOG","Google Inc."}, {"AAPL","Apple Inc."} };

  if (a==b) std::cout << "a and b are equal\n";
  if (b!=c) std::cout << "b and c are not equal\n";

  return 0;
}

Output:

a and b are equal
b and c are not equal

Complexity

Average case: linear in size.
Worst case: quadratic in size.

Iterator validity

No changes.

See also

unordered_map::equal_range: Get range of elements with specific key (public member function)

unordered_map::operator=: Assign content (public member function)

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