mitsch/compile-time-regular-expressions

A Compile time PCRE (almost) compatible regular expression matcher.

Compile time regular expressions v2

Fast compile-time regular expression with support for matching/searching/capturing in compile-time or runtime.

You can use single header version from directory single-header. This header can be regenerated with make single-header.

What this library can do?

ctre::match<"REGEX">(subject); // C++20
"REGEX"_ctre.match(subject); // C++17 + N3599 extension

• Matching
• Searching
• Capturing content (named captures are supported too)

The library is implementing most of the PCRE syntax with a few exceptions:

• atomic groups
• boundaries other than ^$
• callouts
• character properties
• comments
• conditional patterns
• control characters (\cX)
• horizontal / vertical character classes (\h\H\v\V)
• match point reset (\K)
• named characters
• octal numbers
• options / modes
• subroutines
• unicode grapheme cluster (\X)

More documentation on pcre.org.

What can be subject (input)?

• std::string-like object (std::string_view or your own string if it's providing begin/end functions with forward iterators)
• pair of forward iterators

Supported compilers

• clang 5.0+ (template UDL, C++17 syntax)
• gcc 7.2+ (template UDL, C++17 syntax)
• gcc 9.0+ (C++17 & C++20 cNTTP syntax)
• MSVC 15.8.8+ (C++17 syntax only)

Template UDL syntax

Compiler must support N3599 extension, as GNU extension in gcc (not in c++2a mode) and clang.

constexpr auto match(std::string_view sv) noexcept {
	using namespace ctre::literals;
	return "h.*"_ctre.match(sv);
}

C++17 syntax

You can provide pattern as a constexpr ctll::fixed_string variable.

static constexpr auto pattern = ctll::fixed_string{ "h.*" };

constexpr auto match(std::string_view sv) noexcept {
	return ctre::match<pattern>(sv);
}

(this is tested in MSVC 15.8.8)

C++20 syntax

Currently only compiler which supports cNTTP syntax ctre::match<PATTERN>(subject) is GCC 9+. Use -DEXPERIMENTAL_GCC_9 flag to disable trampolining (which crash compiler on ICE).

Also there is known bug in current GCC 9 with debug symbols and cNTTP, you can avoid it if you disable generating debug symbols (-g0).

constexpr auto match(std::string_view sv) noexcept {
	return ctre::match<"h.*">(sv);
}

Examples

Extracting number from input

std::optional<std::string_view> extract_number(std::string_view s) noexcept {
    if (auto m = ctre::match<"^[a-z]++([0-9]++)$">(s)) {
        return m.get<1>().to_view();
    } else {
        return std::nullopt;
    }
}

link to compiler explorer

Extracting values from date

struct date { std::string_view year; std::string_view month; std::string_view day; };

std::optional<date> extract_date(std::string_view s) noexcept {
    using namespace ctre::literals;
    if (auto [whole, year, month, day] = ctre::match<"^(\\d{4})/(\\d{1,2}+)/(\\d{1,2}+)$">(s); whole) {
        return date{year, month, day};
    } else {
        return std::nullopt;
    }
}

//static_assert(extract_date("2018/08/27"sv).has_value());
//static_assert((*extract_date("2018/08/27"sv)).year == "2018"sv);
//static_assert((*extract_date("2018/08/27"sv)).month == "08"sv);
//static_assert((*extract_date("2018/08/27"sv)).day == "27"sv);

link to compiler explorer

Lexer

enum class type {
    unknown, identifier, number
};

struct lex_item {
    type t;
    std::string_view c;
};

std::optional<lex_item> lexer(std::string_view v) noexcept {
    if (auto [m,id,num] = ctre::match<"^([a-z]++)|([0-9]++)$">(v); m) {
        if (id) {
            return lex_item{type::identifier, id};
        } else if (num) {
            return lex_item{type::number, num};
        }
    }
    return std::nullopt;
}

link to compiler explorer

Range over input

This support is preliminary and probably the API will be changed.

auto input = "123,456,768"sv;

for (auto match: ctre::range<"([0-9]++),?">(input)) {
	std::cout << std::string_view{match.get<0>()} << "\n";
}