std::empty
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                    | Defined in header  <iterator> | ||
| Defined in header  <array> | ||
| Defined in header  <deque> | ||
| Defined in header  <forward_list> | ||
| Defined in header  <list> | ||
| Defined in header  <map> | ||
| Defined in header  <regex> | ||
| Defined in header  <set> | ||
| Defined in header  <string> | ||
| Defined in header  <unordered_map> | ||
| Defined in header  <unordered_set> | ||
| Defined in header  <vector> | ||
| 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; | (2) | (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 emptymethod | 
| 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] 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


