| 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 Parameters
| c | - | a container with an empty method |
| array | - | an array of arbitrary type |
| il | - | an initializer list |
Return value
true if the container doesn't have any element.
Exceptions
2,3)
noexcept specification: noexceptPossible 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;
} |
Example
#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
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