std::match_results::max_size
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                    < cpp | regex | match results
                    
                                                            
                    | size_type max_size() const; | (since C++11) | |
Returns the maximum number of submatches the match_results type is able to hold due to system or library implementation limitations, i.e. std::distance(begin(), end()) for the largest number of submatches.
Parameters
(none)
Return value
Maximum number of submatches
Exceptions
noexcept specification:  
noexcept
  Complexity
Constant.