W3cubDocs

/C++

std::regex_constants::error_type

Defined in header <regex>
typedef /*implementation defined*/ error_type;
(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 = /*unspecified*/;
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*/;
(since C++11)
(until C++17)
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 = /*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*/;
(since C++17)

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 one of *?+{ 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

Notes

In C++11, these constants were specified with redundant keyword static, which was removed by C++14 via LWG issue 2053.

Example

Implements regular expressions checker.

#include <iomanip>
#include <iostream>
#include <regex>
#include <sstream>
#include <string>
using namespace std::string_literals;
 
void show_regex_error(const std::regex_error& e) {
    std::string err_message = e.what();
 
#   define CASE(type, msg) \
    case std::regex_constants::type: err_message += " ("s + #type "):\n  "s + msg; \
        break
    switch (e.code()) {
    CASE(error_collate, "The expression contains an invalid collating element name");
    CASE(error_ctype, "The expression contains an invalid character class name");
    CASE(error_escape, "The expression contains an invalid escaped character or a trailing escape");
    CASE(error_backref, "The expression contains an invalid back reference");
    CASE(error_brack, "The expression contains mismatched square brackets ('[' and ']')");
    CASE(error_paren, "The expression contains mismatched parentheses ('(' and ')')");
    CASE(error_brace, "The expression contains mismatched curly braces ('{' and '}')");
    CASE(error_badbrace, "The expression contains an invalid range in a {} expression");
    CASE(error_range, "The expression contains an invalid character range (e.g. [b-a])");
    CASE(error_space, "There was not enough memory to convert the expression into a finite state machine");
    CASE(error_badrepeat, "one of *?+{ was not preceded by a valid regular expression");
    CASE(error_complexity, "The complexity of an attempted match exceeded a predefined level");
    CASE(error_stack, "There was not enough memory to perform a match");
    }
#   undef CASE
 
    /* std::cerr */ std::cout << err_message << ". \n\n";
}
 
void regular_expression_checker(const std::string& text,
                                const std::string& regex,
                                const std::regex::flag_type flags) {
    std::cout << "Text: " << quoted(text) << "\nRegex: " << 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& ex) {
        show_regex_error(ex);
    }
}
 
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 auto your_text = "Hello regular expressions."s;
    const auto your_regex = R"(([a-zA-Z]+) ([a-z]+) ([a-z]+)\.)"s;
    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: "((.)(.)"
Parenthesis is not closed. (error_paren):
  The expression contains mismatched parentheses ('(' and ')').
 
Text: "Invalid!"
Regex: "[."
Unexpected character in bracket expression. (error_brack):
  The expression contains mismatched square brackets ('[' and ']').
 
Text: "Invalid!"
Regex: "[.]{}"
Unexpected token in brace expression. (error_badbrace):
  The expression contains an invalid range in a {} expression.
 
Text: "Invalid!"
Regex: "[1-0]"
Invalid range in bracket expression. (error_range):
  The expression contains an invalid character range (e.g. [b-a]).

See also

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

© cppreference.com
Licensed under the Creative Commons Attribution-ShareAlike Unported License v3.0.
https://en.cppreference.com/w/cpp/regex/error_type