std::unordered_multimap<Key,T,Hash,KeyEqual,Allocator>::begin, std::unordered_multimap<Key,T,Hash,KeyEqual,Allocator>::cbegin - cppreference.com (original) (raw)

Returns an iterator to the first element of *this.

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

[edit] Return value

Iterator to the first element.

[edit] Complexity

Constant.

[edit] Example

#include #include #include #include #include #include   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
2. ∀x ∈ N ∃y ∈ N : x < y
3. ∀x, y ∈ N  : x = y V x ≠ y
4. ∀x ∈ N ∃y ∈ N : y = x + 1 Lemmas:
5. ∀x ∈ N ∃y ∈ N : y = x + 1
6. ∀x ∈ N ∃y ∈ N : x < y
7. ∀x, y ∈ N  : x = y V x ≠ y

[edit] See also

| | returns an iterator to the end (public member function) [edit] | | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | | returns an iterator to the beginning of a container or array (function template) [edit] |