std::match_results<BidirIt,Alloc>::position
Min standard notice:
Returns the position of the first character of the specified sub-match.
# Declarations
difference_type position( size_type n = 0 ) const;
(since C++11)
# Parameters
n: integral number specifying which match to examine
# Return value
The position of the first character of the specified match or sub-match.
# 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::cout << sm.position(1) << '\n';
}