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std::vector<T,Allocator>::empty - cppreference.com

From cppreference.com

bool empty() const;

 (noexcept since C++11)
(constexpr since C++20)

Checks if the container has no elements, i.e. whether begin() == end().

Return value

true if the container is empty, false otherwise.

Complexity

Constant.

Example

#include <iostream>
#include <vector>

int main()
{
    std::cout << std::boolalpha;

    std::vector<int> numbers;
    std::cout << "Initially, numbers.empty(): " << numbers.empty() << '\n';

    numbers.push_back(42);
    std::cout << "After adding elements, numbers.empty(): " << numbers.empty() << '\n';
}

Output: 

Initially, numbers.empty(): true
After adding elements, numbers.empty(): false

See also

returns the number of elements
(public member function) [edit]
checks whether the container is empty
(function template) [edit]