std::empty
From cppreference.com
| Defined in header <iterator>
|
||
| template <class C> constexpr auto empty(const C& c) -> decltype(c.empty()); |
(1) | (since C++17) |
| template <class T, std::size_t N> constexpr bool empty(const T (&array)[N]) noexcept; |
(2) | (since C++17) |
| template <class E> constexpr bool empty(std::initializer_list<E> il) noexcept; |
(3) | (since C++17) |
Returns whether the given container is empty.
1) returns c.empty()
2) returns false
3) returns il.size() == 0
Contents |
[edit] Parameters
| c | - | a container with an empty method
|
| array | - | an array of arbitrary type |
| il | - | an initializer list |
[edit] Return value
true if the container doesn't have any element.
[edit] Exceptions
2,3)
noexcept specification:
noexcept
[edit] Notes
In addition to being included in <iterator>, std::empty is guaranteed to become available if any of the following headers are included: <array>, <deque>, <forward_list>, <list>, <map>, <regex>, <set>, <string>, <unordered_map>, <unordered_set>, and <vector>.
[edit] Possible implementation
| First version |
|---|
template <class C> constexpr auto empty(const C& c) -> decltype(c.empty()) { return c.empty(); } |
| Second version |
template <class T, std::size_t N> constexpr bool empty(const T (&array)[N]) noexcept { return false; } |
| Third version |
template <class E> constexpr bool empty(std::initializer_list<E> il) noexcept { return il.size() == 0; } |
[edit] Example
Run this code
#include <iostream> #include <vector> template <class T> void print(const T& container) { if ( !std::empty(container) ) { std::cout << "Elements:\n"; for ( const auto& element : container ) std::cout << element << '\n'; } else { std::cout << "Empty\n"; } } int main() { std::vector<int> c = { 1, 2, 3 }; print(c); c.clear(); print(c); int array[] = { 4, 5, 6 }; print(array); auto il = { 7, 8, 9 }; print(il); }
Output:
Elements: 1 2 3 Empty Elements: 4 5 6 Elements: 7 8 9