std::regex_constants::error_type(3)

NAME
std::regex_constants::error_type - std::regex_constants::error_type

Synopsis
   Defined in header <regex>
   using error_type = /* implementation-defined */; (1) (since C++11)
   constexpr error_type error_collate = /*
   unspecified */;
   constexpr error_type error_ctype = /*
   unspecified */;
   constexpr error_type error_escape = /*
   unspecified */;
   constexpr error_type error_backref = /*
   unspecified */;
   constexpr error_type error_brack = /*
   unspecified */;
   constexpr error_type error_paren = /*
   unspecified */;
   constexpr error_type error_brace = /* (since C++11)
   unspecified */; (until C++17)
   constexpr error_type error_badbrace = /*
   unspecified */;
   constexpr error_type error_range = /*
   unspecified */;
   constexpr error_type error_space = /*
   unspecified */;
   constexpr error_type error_badrepeat = /*
   unspecified */;
   constexpr error_type error_complexity = /*
   unspecified */;
   constexpr error_type error_stack = /*
   unspecified */; (2)
   inline constexpr error_type error_collate = /*
   unspecified */;
   inline constexpr error_type error_ctype = /*
   unspecified */;
   inline constexpr error_type error_escape = /*
   unspecified */;
   inline constexpr error_type error_backref = /*
   unspecified */;
   inline constexpr error_type error_brack = /*
   unspecified */;
   inline constexpr error_type error_paren = /*
   unspecified */;
   inline constexpr error_type error_brace = /* (since C++17)
   unspecified */;
   inline constexpr error_type error_badbrace = /*
   unspecified */;
   inline constexpr error_type error_range = /*
   unspecified */;
   inline constexpr error_type error_space = /*
   unspecified */;
   inline constexpr error_type error_badrepeat = /*
   unspecified */;
   inline constexpr error_type error_complexity = /*
   unspecified */;
   inline constexpr error_type error_stack = /*
   unspecified */;
   1) The error_type is a type that describes errors that may occur during regular
   expression parsing.

Constants
   Constant Explanation
   error_collate the expression contains an invalid collating element name
   error_ctype the expression contains an invalid character class name
   error_escape the expression contains an invalid escaped character or a trailing
                    escape
   error_backref the expression contains an invalid back reference
   error_brack the expression contains mismatched square brackets ('[' and ']')
   error_paren the expression contains mismatched parentheses ('(' and ')')
   error_brace the expression contains mismatched curly braces ('{' and '}')
   error_badbrace the expression contains an invalid range in a {} expression
   error_range the expression contains an invalid character range (e.g. [b-a])
   error_space there was not enough memory to convert the expression into a finite
                    state machine
   error_badrepeat '*', '?', '+' or '{' was not preceded by a valid regular expression
   error_complexity the complexity of an attempted match exceeded a predefined level
   error_stack there was not enough memory to perform a match

Example
   Implements regular expressions checker: // Run this code
 #include <cstddef>
 #include <iomanip>
 #include <iostream>
 #include <regex>
 #include <sstream>
 #include <string>
 void regular_expression_checker(const std::string& text,
                        const std::string& regex,
                        const std::regex::flag_type flags)
 {
     std::cout << "Text: " << std::quoted(text) << '\n'
               << "Regex: " << std::quoted(regex) << '\n';
     try
     {
         const std::regex re{regex, flags};
         const bool matched = std::regex_match(text, re);
         std::stringstream out;
         out << (matched ? "MATCH!\n" : "DOES NOT MATCH!\n");
         std::smatch m;
         if (std::regex_search(text, m, re); !m.empty())
         {
             out << "prefix = [" << m.prefix().str().data() << "]\n";
             for (std::size_t i{}; i != m.size(); ++i)
                 out << " m[" << i << "] = [" << m[i].str().data() << "]\n";
             out << "suffix = [" << m.suffix().str().data() << "]\n";
         }
         std::cout << out.str() << '\n';
     }
     catch (std::regex_error& e)
     {
         std::cout << "Error: " << e.what() << ".\n\n";
     }
 }
 int main()
 {
     constexpr std::regex::flag_type your_flags
         = std::regex::flag_type{0}
     // Choose one of the supported grammars:
         | std::regex::ECMAScript
     // | std::regex::basic
     // | std::regex::extended
     // | std::regex::awk
     // | std::regex::grep
     // | std::regex::egrep
     // Choose any of the next options:
     // | std::regex::icase
     // | std::regex::nosubs
     // | std::regex::optimize
     // | std::regex::collate
     // | std::regex::multiline
         ;
     const std::string your_text = "Hello regular expressions.";
     const std::string your_regex = R"(([a-zA-Z]+) ([a-z]+) ([a-z]+)\.)";
     regular_expression_checker(your_text, your_regex, your_flags);
     regular_expression_checker("Invalid!", R"(((.)(.))", your_flags);
     regular_expression_checker("Invalid!", R"([.)", your_flags);
     regular_expression_checker("Invalid!", R"([.]{})", your_flags);
     regular_expression_checker("Invalid!", R"([1-0])", your_flags);
 }

Possible output:
 Text: "Hello regular expressions."
 Regex: "([a-zA-Z]+) ([a-z]+) ([a-z]+)\\."
 MATCH!
 prefix = []
   m[0] = [Hello regular expressions.]
   m[1] = [Hello]
   m[2] = [regular]
   m[3] = [expressions]
 suffix = []
 Text: "Invalid!"
 Regex: "((.)(.)"
 Error: Mismatched '(' and ')' in regular expression.
 Text: "Invalid!"
 Regex: "[."
 Error: Unexpected character within '[...]' in regular expression.
 Text: "Invalid!"
 Regex: "[.]{}"
 Error: Invalid range in '{}' in regular expression.
 Text: "Invalid!"
 Regex: "[1-0]"
 Error: Invalid range in bracket expression..
   Defect reports
   The following behavior-changing defect reports were applied retroactively to
   previously published C++ standards.
      DR Applied to Behavior as published Correct behavior
   LWG 2053 C++11 the constants were declared static removed the static specifier

See also
   regex_error reports errors generated by the regular expressions library
   (C++11) (class)