NAME¶

std::unordered_multimap::begin, - std::unordered_multimap::begin,

Synopsis¶

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¶

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