std::string_view empty() method

since C++20

// Const version only
[[nodiscard]] constexpr bool empty() const noexcept;

since C++17

// Const version only
constexpr bool empty() const noexcept;

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

Parameters

(none)

Return value

true if the container is empty, false otherwise.

Complexity

Constant - O(1).

Why [[nodiscard]]?

The [[nodiscard]] attribute is an attribute that invokes compiler warnings whenever a function has been called and it's result has been discarded.

The reason behind the attribute being applied only to the empty method is that it's likely that the programmer might confuse the adjective empty (which would mean - is this container empty?) for the verb empty (which would mean - please empty this container for me.).

Example

Main.cpp

#include <string_view>
#include <iostream>
 
void check_string(std::string_view ref)
{
        // Print a string surrounded by single quotes, its length
        // and whether it is considered empty.
        std::cout << std::boolalpha
                  << "'" << ref << "' has " << ref.size()
                  << " character(s); emptiness: " << ref.empty() << '\n';
}
 
int main(int argc, char **argv)
{
        // An empty string
        check_string("");
 
        // Almost always not empty: argv[0]
        if (argc > 0)
                check_string(argv[0]);
}

Possible output

'' has 0 character(s); emptiness: true
'./a.out' has 7 character(s); emptiness: false