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

From cppreference.com

C++
Containers library
std::unordered_multimap
Member types
Member functions
Non-member functions
Deduction guides (C++17)
iterator begin ( ) noexcept ;
(1) (since C++11)
const_iterator begin ( ) const noexcept ;
(2) (since C++11)
const_iterator cbegin ( ) const noexcept ;
(3) (since C++11)

Returns an iterator to the first element of the unordered_multimap .

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

range-begin-end.svg

Parameters

(none)

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 = [](const std::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(), [&](const auto& 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

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