std::match_results<BidirIt,Alloc>:: operator[]

If n > 0 and n < size ( ) , returns a reference to the std::sub_match representing the part of the target sequence that was matched by the n ^th captured marked subexpression ).

If n == 0 , returns a reference to the std::sub_match representing the part of the target sequence matched by the entire matched regular expression.

if n >= size ( ) , returns a reference to a std::sub_match representing an unmatched sub-expression (an empty subrange of the target sequence).

The behavior is undefined unless ready ( ) == true .

Parameters

Return value

Reference to the std::sub_match representing the specified matched subrange within the target sequence.

Example

#include <iostream>
#include <regex>
#include <string>
 
int main()
{
    std::string target("baaaby");
    std::smatch sm;
 
    std::regex re1("a(a)*b");
    std::regex_search(target, sm, re1);
    std::cout << "entire match: " << sm[0] << '\n'
              << "submatch #1: " << sm[1] << '\n';
 
    std::regex re2("a(a*)b");
    std::regex_search(target, sm, re2);
    std::cout << "entire match: " << sm[0] << '\n'
              << "submatch #1: " << sm[1] << '\n';
}

entire match: aaab
submatch #1: a
entire match: aaab
submatch #1: aa

See also