std::unordered_multimap<Key,T,Hash,KeyEqual,Allocator>::begin, std::unordered_multimap<Key,T,Hash,KeyEqual,Allocator>::cbegin

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros(C++20)

Language support library

Concepts library(C++20)

Diagnostics library

Memory management library

Metaprogramming library(C++11)

General utilities library

Containers library

Iterators library

Ranges library(C++20)

Algorithms library

Strings library

Text processing library

Numerics library

Date and time library

Input/output library

Filesystem library(C++17)

Concurrency support library(C++11)

Execution control library(C++26)

Technical specifications

Symbols index

External libraries

 

Containers library

node-handle (C++17)

Sequence

array (C++11)

vector

vector<bool>

inplace_vector (C++26)

hive (C++26)

deque

forward_list (C++11)

list

Associative

set

multiset

map

multimap

Unordered associative

unordered_set (C++11)

unordered_multiset (C++11)

unordered_map (C++11)

unordered_multimap (C++11)

Adaptors

stack

queue

priority_queue

flat_set (C++23)

flat_multiset (C++23)

flat_map (C++23)

flat_multimap (C++23)

Views

span (C++20)

mdspan (C++23)

Tables

Iterator invalidation

Member function table

Non-member function table

 

std::unordered_multimap

Member types
Member functions
unordered_multimap::unordered_multimap unordered_multimap::~unordered_multimap    unordered_multimap::operator= unordered_multimap::get_allocator Iterators unordered_multimap::beginunordered_multimap::cbegin unordered_multimap::endunordered_multimap::cend Capacity unordered_multimap::size unordered_multimap::max_size unordered_multimap::empty Modifiers unordered_multimap::clear unordered_multimap::insert unordered_multimap::insert_range (C++23) unordered_multimap::emplace unordered_multimap::emplace_hint unordered_multimap::erase unordered_multimap::swap unordered_multimap::extract (C++17) unordered_multimap::merge (C++17)	Lookup unordered_multimap::count unordered_multimap::find unordered_multimap::contains (C++20) unordered_multimap::equal_range Bucket interface unordered_multimap::begin(size_type)unordered_multimap::cbegin(size_type) unordered_multimap::end(size_type)unordered_multimap::cend(size_type) unordered_multimap::bucket_count unordered_multimap::max_bucket_count unordered_multimap::bucket_size unordered_multimap::bucket Hash policy unordered_multimap::load_factor unordered_multimap::max_load_factor unordered_multimap::rehash unordered_multimap::reserve Observers unordered_multimap::hash_function unordered_multimap::key_eq
Non-member functions
std::swap(std::unordered_multimap) erase_if(std::unordered_multimap) (C++20)	operator==operator!= (until C++20)
Deduction guides(C++17)

 

iterator begin()noexcept;	(1)	(since C++11) (constexpr since C++26)
const_iterator begin()constnoexcept;	(2)	(since C++11) (constexpr since C++26)
const_iterator cbegin()constnoexcept;	(3)	(since C++11) (constexpr since C++26)

Returns an iterator to the first element of *this.

If *this is empty, the returned iterator will be equal to end().

Return value

Iterator to the first element.

Complexity

Constant.

Example

Run this code

#include <algorithm>#include <cassert>#include <iostream>#include <string>#include <utility>#include <unordered_map>   int main(){auto show_node =[](conststd::pair<std::string, std::string>& node){std::cout<< node.first<<" : "<< node.second<<'\n';};   std::unordered_multimap<std::string, std::string> lemmas;assert(lemmas.begin()== lemmas.end());assert(lemmas.cbegin()== lemmas.cend());   lemmas.insert({"1. ∀x ∈ N ∃y ∈ N", "x ≤ y"}); show_node(*lemmas.cbegin());assert(lemmas.begin()!= lemmas.end());assert(lemmas.cbegin()!= lemmas.cend());   lemmas.begin()->second ="x < y"; show_node(*lemmas.cbegin());   lemmas.insert({"2. ∀x, y ∈ N ", "x = y V x ≠ y"}); show_node(*lemmas.cbegin());   lemmas.insert({"3. ∀x ∈ N ∃y ∈ N", "y = x + 1"}); show_node(*lemmas.cbegin());   std::cout<<"Lemmas: \n";std::for_each(lemmas.cbegin(), lemmas.cend(), [&](constauto& n){ show_node(n);});std::cout<<'\n';}

Possible output:

1. ∀x ∈ N ∃y ∈ N : x ≤ y 1. ∀x ∈ N ∃y ∈ N : x < y 2. ∀x, y ∈ N  : x = y V x ≠ y 3. ∀x ∈ N ∃y ∈ N : y = x + 1 Lemmas: 3. ∀x ∈ N ∃y ∈ N : y = x + 1 1. ∀x ∈ N ∃y ∈ N : x < y 2. ∀x, y ∈ N  : x = y V x ≠ y

See also

endcend	returns an iterator to the end (public member function)
begincbegin (C++11)(C++14)	returns an iterator to the beginning of a container or array (function template)