std::match_results::operator[] - cppreference.com

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# std::match_results::operator[]

From cppreference.com
< cpp‎ | regex‎ | match results

const_reference operator[]( size_type n ) const; |  | (since C++11)

Returns an indicated sub-match.

If n == 0, entire matched expression is returned.

If n > 0 && n < size(), nth sub-match is returned.

if n >= size(), a sub-match representing the unmatched match is returned.

### [edit] Parameters

n | - | integral number specifying which match to return

### [edit] Return value

Returns a sub-match representing the specified match or sub match.

### [edit] Example

Run this code

    #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';

    }

Output:

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

### [edit] See also

str | returns the sequence of characters for the particular sub-match (public member function) [edit]

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