std::sub_match<BidirIt>::sub_match - cppreference.com

From cppreference.com

constexpr sub_match();

(since C++11)

Default constructs a std::sub_match. The matched member is set to false and the inherited members first and second are value-initialized.

This is the only publicly accessible and defined constructor.

Example

#include <cassert>
#include <regex>

int main()
{
    std::sub_match<const char*> s;
    assert(!s.matched);
}