std::unordered_multimap<Key,T,Hash,KeyEqual,Allocator>::begin,std::unordered_multimap<Key,T,Hash,KeyEqual,Allocator>::cbegin
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C++
Containers library
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| Sequence | ||||
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(C++26) | ||||
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| Associative | ||||
| Unordered associative | ||||
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| Iterator invalidation | ||||
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| Non-member function table |
std::unordered_multimap| Member types | ||||||
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| Deduction guides(C++17) | ||||||
iterator begin()noexcept; | (1) | (since C++11) (constexpr since C++26) |
const_iterator begin()constnoexcept; | (2) | (since C++11) (constexpr since C++26) |
const_iterator cbegin()constnoexcept; | (3) | (since C++11) (constexpr since C++26) |
Returns an iterator to the first element of*this.
If*this is empty, the returned iterator will be equal toend().
Contents |
[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=[](conststd::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(),[&](constauto& n){ show_node(n);});std::cout<<'\n';}
Possible output:
1. ∀x ∈ N ∃y ∈ N : x ≤ y1. ∀x ∈ N ∃y ∈ N : x < y2. ∀x, y ∈ N : x = y V x ≠ y3. ∀x ∈ N ∃y ∈ N : y = x + 1Lemmas: 3. ∀x ∈ N ∃y ∈ N : y = x + 11. ∀x ∈ N ∃y ∈ N : x < y2. ∀x, y ∈ N : x = y V x ≠ y
[edit]See also
| returns an iterator to the end (public member function)[edit] | |
(C++11)(C++14) | returns an iterator to the beginning of a container or array (function template)[edit] |
