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‎docs/standard-library/map-class.md‎

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‎docs/standard-library/multimap-class.md‎

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‎docs/standard-library/multiset-class.md‎

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‎docs/standard-library/set-class.md‎

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‎docs/standard-library/unordered-map-class.md‎

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---
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title: "unordered_map Class"
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ms.date: "11/04/2016"
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f1_keywords: ["unordered_map/std::unordered_map", "unordered_map/std::unordered_map::allocator_type", "unordered_map/std::unordered_map::const_iterator", "unordered_map/std::unordered_map::const_local_iterator", "unordered_map/std::unordered_map::const_pointer", "unordered_map/std::unordered_map::const_reference", "unordered_map/std::unordered_map::difference_type", "unordered_map/std::unordered_map::hasher", "unordered_map/std::unordered_map::iterator", "unordered_map/std::unordered_map::key_equal", "unordered_map/std::unordered_map::key_type", "unordered_map/std::unordered_map::local_iterator", "unordered_map/std::unordered_map::mapped_type", "unordered_map/std::unordered_map::pointer", "unordered_map/std::unordered_map::reference", "unordered_map/std::unordered_map::size_type", "unordered_map/std::unordered_map::value_type", "unordered_map/std::unordered_map::at", "unordered_map/std::unordered_map::begin", "unordered_map/std::unordered_map::bucket", "unordered_map/std::unordered_map::bucket_count", "unordered_map/std::unordered_map::bucket_size", "unordered_map/std::unordered_map::cbegin", "unordered_map/std::unordered_map::cend", "unordered_map/std::unordered_map::clear", "unordered_map/std::unordered_map::count", "unordered_map/std::unordered_map::emplace", "unordered_map/std::unordered_map::emplace_hint", "unordered_map/std::unordered_map::empty", "unordered_map/std::unordered_map::end", "unordered_map/std::unordered_map::equal_range", "unordered_map/std::unordered_map::erase", "unordered_map/std::unordered_map::find", "unordered_map/std::unordered_map::get_allocator", "unordered_map/std::unordered_map::hash", "unordered_map/std::unordered_map::insert", "unordered_map/std::unordered_map::key_eq", "unordered_map/std::unordered_map::load_factor", "unordered_map/std::unordered_map::max_bucket_count", "unordered_map/std::unordered_map::max_load_factor", "unordered_map/std::unordered_map::max_size", "unordered_map/std::unordered_map::rehash", "unordered_map/std::unordered_map::size", "unordered_map/std::unordered_map::swap", "unordered_map/std::unordered_map::unordered_map", "unordered_map/std::unordered_map::hash_function"]
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helpviewer_keywords: ["std::unordered_map", "std::unordered_map::allocator_type", "std::unordered_map::const_iterator", "std::unordered_map::const_local_iterator", "std::unordered_map::const_pointer", "std::unordered_map::const_reference", "std::unordered_map::difference_type", "std::unordered_map::hasher", "std::unordered_map::iterator", "std::unordered_map::key_equal", "std::unordered_map::key_type", "std::unordered_map::local_iterator", "std::unordered_map::mapped_type", "std::unordered_map::pointer", "std::unordered_map::reference", "std::unordered_map::size_type", "std::unordered_map::value_type", "std::unordered_map::at", "std::unordered_map::begin", "std::unordered_map::bucket", "std::unordered_map::bucket_count", "std::unordered_map::bucket_size", "std::unordered_map::cbegin", "std::unordered_map::cend", "std::unordered_map::clear", "std::unordered_map::count", "std::unordered_map::emplace", "std::unordered_map::emplace_hint", "std::unordered_map::empty", "std::unordered_map::end", "std::unordered_map::equal_range", "std::unordered_map::erase", "std::unordered_map::find", "std::unordered_map::get_allocator", "std::unordered_map::hash", "std::unordered_map::insert", "std::unordered_map::key_eq", "std::unordered_map::load_factor", "std::unordered_map::max_bucket_count", "std::unordered_map::max_load_factor", "std::unordered_map::max_size", "std::unordered_map::rehash", "std::unordered_map::size", "std::unordered_map::swap", "std::unordered_map::unordered_map", "std::unordered_map::allocator_type", "std::unordered_map::const_iterator", "std::unordered_map::const_local_iterator", "std::unordered_map::const_pointer", "std::unordered_map::const_reference", "std::unordered_map::difference_type", "std::unordered_map::hasher", "std::unordered_map::iterator", "std::unordered_map::key_equal", "std::unordered_map::key_type", "std::unordered_map::local_iterator", "std::unordered_map::mapped_type", "std::unordered_map::pointer", "std::unordered_map::reference", "std::unordered_map::size_type", "std::unordered_map::value_type", "std::unordered_map::at", "std::unordered_map::begin", "std::unordered_map::bucket", "std::unordered_map::bucket_count", "std::unordered_map::bucket_size", "std::unordered_map::cbegin", "std::unordered_map::cend", "std::unordered_map::clear", "std::unordered_map::count", "std::unordered_map::emplace", "std::unordered_map::emplace_hint", "std::unordered_map::empty", "std::unordered_map::end", "std::unordered_map::equal_range", "std::unordered_map::erase", "std::unordered_map::find", "std::unordered_map::get_allocator", "std::unordered_map::hash_function", "std::unordered_map::insert", "std::unordered_map::key_eq", "std::unordered_map::load_factor", "std::unordered_map::max_bucket_count", "std::unordered_map::max_load_factor", "std::unordered_map::max_size", "std::unordered_map::rehash", "std::unordered_map::size", "std::unordered_map::swap"]
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description: "API reference for the C++ Standard Library container class `unordered_map`, which controls a varying-length sequence of elements."
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ms.date: "9/9/2020"
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f1_keywords: ["unordered_map/std::unordered_map", "unordered_map/std::unordered_map::allocator_type", "unordered_map/std::unordered_map::const_iterator", "unordered_map/std::unordered_map::const_local_iterator", "unordered_map/std::unordered_map::const_pointer", "unordered_map/std::unordered_map::const_reference", "unordered_map/std::unordered_map::difference_type", "unordered_map/std::unordered_map::hasher", "unordered_map/std::unordered_map::iterator", "unordered_map/std::unordered_map::key_equal", "unordered_map/std::unordered_map::key_type", "unordered_map/std::unordered_map::local_iterator", "unordered_map/std::unordered_map::mapped_type", "unordered_map/std::unordered_map::pointer", "unordered_map/std::unordered_map::reference", "unordered_map/std::unordered_map::size_type", "unordered_map/std::unordered_map::value_type", "unordered_map/std::unordered_map::at", "unordered_map/std::unordered_map::begin", "unordered_map/std::unordered_map::bucket", "unordered_map/std::unordered_map::bucket_count", "unordered_map/std::unordered_map::bucket_size", "unordered_map/std::unordered_map::cbegin", "unordered_map/std::unordered_map::cend", "unordered_map/std::unordered_map::clear", "unordered_map/std::unordered_map::contains", "unordered_map/std::unordered_map::count", "unordered_map/std::unordered_map::emplace", "unordered_map/std::unordered_map::emplace_hint", "unordered_map/std::unordered_map::empty", "unordered_map/std::unordered_map::end", "unordered_map/std::unordered_map::equal_range", "unordered_map/std::unordered_map::erase", "unordered_map/std::unordered_map::find", "unordered_map/std::unordered_map::get_allocator", "unordered_map/std::unordered_map::hash", "unordered_map/std::unordered_map::insert", "unordered_map/std::unordered_map::key_eq", "unordered_map/std::unordered_map::load_factor", "unordered_map/std::unordered_map::max_bucket_count", "unordered_map/std::unordered_map::max_load_factor", "unordered_map/std::unordered_map::max_size", "unordered_map/std::unordered_map::rehash", "unordered_map/std::unordered_map::size", "unordered_map/std::unordered_map::swap", "unordered_map/std::unordered_map::unordered_map", "unordered_map/std::unordered_map::hash_function"]
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helpviewer_keywords: ["std::unordered_map", "std::unordered_map::allocator_type", "std::unordered_map::const_iterator", "std::unordered_map::const_local_iterator", "std::unordered_map::const_pointer", "std::unordered_map::const_reference", "std::unordered_map::difference_type", "std::unordered_map::hasher", "std::unordered_map::iterator", "std::unordered_map::key_equal", "std::unordered_map::key_type", "std::unordered_map::local_iterator", "std::unordered_map::mapped_type", "std::unordered_map::pointer", "std::unordered_map::reference", "std::unordered_map::size_type", "std::unordered_map::value_type", "std::unordered_map::at", "std::unordered_map::begin", "std::unordered_map::bucket", "std::unordered_map::bucket_count", "std::unordered_map::bucket_size", "std::unordered_map::cbegin", "std::unordered_map::cend", "std::unordered_map::clear", "std::unordered_map::contains", "std::unordered_map::count", "std::unordered_map::emplace", "std::unordered_map::emplace_hint", "std::unordered_map::empty", "std::unordered_map::end", "std::unordered_map::equal_range", "std::unordered_map::erase", "std::unordered_map::find", "std::unordered_map::get_allocator", "std::unordered_map::hash", "std::unordered_map::insert", "std::unordered_map::key_eq", "std::unordered_map::load_factor", "std::unordered_map::max_bucket_count", "std::unordered_map::max_load_factor", "std::unordered_map::max_size", "std::unordered_map::rehash", "std::unordered_map::size", "std::unordered_map::swap", "std::unordered_map::unordered_map", "std::unordered_map::allocator_type", "std::unordered_map::const_iterator", "std::unordered_map::const_local_iterator", "std::unordered_map::const_pointer", "std::unordered_map::const_reference", "std::unordered_map::difference_type", "std::unordered_map::hasher", "std::unordered_map::iterator", "std::unordered_map::key_equal", "std::unordered_map::key_type", "std::unordered_map::local_iterator", "std::unordered_map::mapped_type", "std::unordered_map::pointer", "std::unordered_map::reference", "std::unordered_map::size_type", "std::unordered_map::value_type", "std::unordered_map::at", "std::unordered_map::begin", "std::unordered_map::bucket", "std::unordered_map::bucket_count", "std::unordered_map::bucket_size", "std::unordered_map::cbegin", "std::unordered_map::cend", "std::unordered_map::clear", "std::unordered_map::count", "std::unordered_map::emplace", "std::unordered_map::emplace_hint", "std::unordered_map::empty", "std::unordered_map::end", "std::unordered_map::equal_range", "std::unordered_map::erase", "std::unordered_map::find", "std::unordered_map::get_allocator", "std::unordered_map::hash_function", "std::unordered_map::insert", "std::unordered_map::key_eq", "std::unordered_map::load_factor", "std::unordered_map::max_bucket_count", "std::unordered_map::max_load_factor", "std::unordered_map::max_size", "std::unordered_map::rehash", "std::unordered_map::size", "std::unordered_map::swap"]
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ms.assetid: 7cf7cfa1-16e7-461c-a9b2-3b8d8ec24e0d
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# unordered_map Class
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|[cend](#cend)|Designates the end of the controlled sequence.|
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|[clear](#clear)|Removes all elements.|
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|[count](#count)|Finds the number of elements matching a specified key.|
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|[contains](#contains)<sup>C++20</sup>|Check if there is an element with the specified key in the `unordered_map`.|
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|[emplace](#emplace)|Adds an element constructed in place.|
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|[emplace_hint](#emplace_hint)|Adds an element constructed in place, with hint.|
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|[empty](#empty)|Tests whether no elements are present.|
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[c, 3] [b, 2] [a, 1]
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```
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## <a name="contains"></a> unordered_map::contains
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Checks if there is an element in the `unordered_map` with the specified key.
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Introduced in C++20.
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```cpp
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bool contains(const Key& key) const;
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<class K> bool contains(const K& key) const;
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```
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### Parameters
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*K*\
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The type of the key.
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*key*\
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The key value of the element to look for.
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### Return Value
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`true` if the element is found in the container; `false` otherwise.
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### Remarks
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`contains()` is new in C++20. To use it, specify the [/std:c++latest](../build/reference/std-specify-language-standard-version.md) compiler option.
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`template<class K> bool contains(const K& key) const` only participates in overload resolution if `key_compare` is transparent.
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### Example
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```cpp
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// Requires /std:c++latest
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#include <unordered_map>
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#include <iostream>
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int main()
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{
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std::unordered_map<int, bool> theUnorderedMap = {{0, false}, {1,true}};
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std::cout << std::boolalpha; // so booleans show as 'true' or 'false'
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std::cout << theUnorderedMap.contains(1) << '\n';
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std::cout << theUnorderedMap.contains(2) << '\n';
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return 0;
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}
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```
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```Output
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true
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false
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```
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## <a name="count"></a> unordered_map::count
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Finds the number of elements matching a specified key.

‎docs/standard-library/unordered-map.md‎

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title: "&lt;unordered_map&gt;"
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description: "API overview for the C++ Standard Library container class `map`."
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ms.date: "11/04/2016"
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f1_keywords: ["<unordered_map>"]
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helpviewer_keywords: ["unordered_map header"]

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