size_type size() const; (since C++11)
Returns the number of submatches, i.e. std::distance(begin(), end()).
Parameters
(none).
Return value
The number of submatches.
Exceptions
noexcept specification: noexcept
Complexity
Constant.
See also
Example
#include <iostream>
#include <regex>
#include <string>
int main()
{
std::regex re("a(a)*b");
std::string target("aaab");
std::smatch sm;
std::regex_match(target, sm, re);
std::cou