std::map<Key,T,Compare,Allocator>::empty
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bool empty() const;
(noexcept since C++11) (constexpr since C++26)
Checks if the container has no elements.
Contents
[edit] Return value
true if the container is empty, false otherwise.
[edit] Complexity
Constant.
[edit] Example
The following code uses empty to check if a std::map <int, int> contains any elements:
Run this code
#include <iostream> #include <map> #include <utility> int main() { std::map <int,int> numbers; std::cout << std::boolalpha ; std::cout << "Initially, numbers.empty(): " << numbers.empty() << '\n'; numbers.emplace(42, 13); numbers.insert(std::make_pair (13317, 123)); std::cout << "After adding elements, numbers.empty(): " << numbers.empty() << '\n'; }
Output:
Initially, numbers.empty(): true After adding elements, numbers.empty(): false