Difference between revisions of "cpp/container/unordered multimap/begin"
From cppreference.com
< cpp | container | unordered multimap
m (Shorten template names. Use {{lc}} where appropriate.) |
m (langlinks) |
||
| Line 1: | Line 1: | ||
{{include page|cpp/container/begin|unordered_multimap}} | {{include page|cpp/container/begin|unordered_multimap}} | ||
| − | + | {{langlinks|de|es|fr|it|ja|pt|ru|zh}} | |
| − | + | ||
| − | + | ||
| − | + | ||
| − | + | ||
| − | + | ||
| − | + | ||
| − | + | ||
Latest revision as of 10:51, 4 December 2021
| 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().
Contents |
[edit] Parameters
(none)
[edit] Return value
Iterator to the first element.
[edit] Complexity
Constant.
[edit] 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
[edit] 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) |
