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/C++std::unordered_multimap<Key,T,Hash,KeyEqual,Allocator>::begin, std::unordered_multimap<Key,T,Hash,KeyEqual,Allocator>::cbegin
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().
Parameters
(none).
Return value
Iterator to the first element.
Complexity
Constant.
Example
#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
|
(C++11) | 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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