std::unordered_multimap<Key,T,Hash,KeyEqual,Allocator>::begin, std::unordered_multimap<Key,T,Hash,KeyEqual,Allocator>::cbegin
From cppreference.com
< cpp | container | unordered multimap
| iterator begin() noexcept; |
(since C++11) | |
| const_iterator begin() const noexcept; |
(since C++11) | |
| const_iterator cbegin() const noexcept; |
(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
Run this code
#include <unordered_map> #include <algorithm> #include <cassert> #include <iostream> #include <string> #include <utility> 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()); // OK assert(lemmas.cbegin() == lemmas.cend()); // OK lemmas.insert({ "1. ∀x ∈ N ∃y ∈ N", "x ≤ y" }); show_node(*lemmas.cbegin()); assert(lemmas.begin() != lemmas.end()); // OK assert(lemmas.cbegin() != lemmas.cend()); // OK 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) |