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https://github.com/hanickadot/compile-time-regular-expressions

Compile Time Regular Expression in C++
https://github.com/hanickadot/compile-time-regular-expressions

awesome compile-time constexpr cpp17 cpp20 header-only pcre regular-expression template-udl

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Compile Time Regular Expression in C++

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# Compile time regular expressions v3



[![Build Status](https://travis-ci.org/hanickadot/compile-time-regular-expressions.svg?branch=master)](https://travis-ci.org/hanickadot/compile-time-regular-expressions)



Fast compile-time regular expressions with support for matching/searching/capturing during compile-time or runtime.



You can use the single header version from directory `single-header`. This header can be regenerated with `make single-header`. If you are using cmake, you can add this directory as subdirectory and link to target `ctre`.



More info at [compile-time.re](https://compile-time.re/)



## What this library can do



```c++

ctre::match<"REGEX">(subject); // C++20

"REGEX"_ctre.match(subject); // C++17 + N3599 extension

```



* Matching

* Searching (`search` or `starts_with`)

* Capturing content (named captures are supported too)

* Back-Reference (\g{N} syntax, and \1...\9 syntax too)

* Multiline support (with `multi_`) functions

* Unicode properties and UTF-8 support



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



* callouts

* comments

* conditional patterns

* control characters (`\cX`)

* match point reset (`\K`)

* named characters

* octal numbers

* options / modes

* subroutines

* unicode grapheme cluster (`\X`)



More documentation on [pcre.org](https://www.pcre.org/current/doc/html/pcre2syntax.html).



### Unknown character escape behaviour



Not all escaped characters are automatically inserted as self, behaviour of the library is escaped characters are with special meaning, unknown escaped character is a syntax error.



Explicitly allowed character escapes which insert only the character are:



```\-\"\<\>```



## Basic API



This is approximated API specification from a user perspective (omitting `constexpr` and `noexcept` which are everywhere, and using C++20 syntax even the API is C++17 compatible):

```c++

// look if whole input matches the regex:

template  auto ctre::match(auto Range &&) -> regex_results;

template  auto ctre::match(auto First &&, auto Last &&) -> regex_results;



// look if input contains match somewhere inside of itself:

template  auto ctre::search(auto Range &&) -> regex_results;

template  auto ctre::search(auto First &&, auto Last &&) -> regex_results;



// check if input starts with match (but doesn't need to match everything):

template  auto ctre::starts_with(auto Range &&) -> regex_results;

template  auto ctre::starts_with(auto First &&, auto Last &&) -> regex_results;



// result type is deconstructible into a structured bindings

template <...> struct regex_results {

	operator bool() const; // if it's a match

	auto to_view() const -> std::string_view; // also view()

	auto to_string() const -> std::string; // also str()

	operator std::string_view() const; // also supports all char variants

	explicit operator std::string() const;

	

	// also size(), begin(), end(), data()

	

	size_t count() const; // number of captures 

	template  const captured_content & get() const; // provide specific capture, whole regex_results is implicit capture 0

};

```



### Range outputing API



```c++

// search for regex in input and return each occurence, ignoring rest:

template  auto ctre::range(auto Range &&) -> range of regex_result;

template  auto ctre::range(auto First &&, auto Last &&) -> range of regex_result;



// return range of each match, stopping at something which can't be matched

template  auto ctre::tokenize(auto Range &&) -> range of regex_result;

template  auto ctre::tokenize(auto First &&, auto Last &&) -> range of regex_result;



// return parts of the input splited by the regex, returning it as part of content of the implicit zero capture (other captures are not changed, you can use it to access how the values were splitted):

template  auto ctre::split(auto Range &&) -> regex_result;

template  auto ctre::split(auto First &&, auto Last &&) -> range of regex_result;

```



### Functors



All the functions (`ctre::match`, `ctre::search`, `ctre::starts_with`, `ctre::range`, `ctre::tokenize`, `ctre::split`) are functors and can be used without parenthesis:



```c++

auto matcher = ctre::match<"regex">;

if (matcher(input)) ...

```



### Possible subjects (inputs)



* `std::string`-like objects (`std::string_view` or your own string if it's providing `begin`/`end` functions with forward iterators)

* pairs of forward iterators



### Unicode support



To enable you need to include:

* ``

* or `` and ``



Otherwise you will get missing symbols if you try to use the unicode support without enabling it.



## Supported compilers



* clang 7.0+ (template UDL, C++17 syntax)

* xcode clang 10.0+ (template UDL, C++17 syntax)

* clang 12.0+ (C++17 syntax, C++20 cNTTP syntax)

* gcc 8.0+ (template UDL, C++17 syntax)

* gcc 9.0+ (C++17 & C++20 cNTTP syntax)

* MSVC 14.29+ (Visual Studio 16.11+) (C++20) 



### Template UDL syntax



The compiler must support extension N3599, for example as GNU extension in gcc (not in GCC 9.1+) and clang.



```c++

constexpr auto match(std::string_view sv) noexcept {

    using namespace ctre::literals;

    return "h.*"_ctre.match(sv);

}

```



If you need extension N3599 in GCC 9.1+, you can't use -pedantic. Also, you need to define macro `CTRE_ENABLE_LITERALS`.



### C++17 syntax



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



```c++

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



constexpr auto match(std::string_view sv) noexcept {

    return ctre::match(sv);

}

```



(this is tested in MSVC 15.8.8)



### C++20 syntax



Currently, the only compiler which supports cNTTP syntax `ctre::match(subject)` is GCC 9+.



```c++

constexpr auto match(std::string_view sv) noexcept {

    return ctre::match<"h.*">(sv);

}

```



## Examples



### Extracting number from input



```c++

std::optional 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](https://gcc.godbolt.org/z/5U67_e)



### Extracting values from date



```c++

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



std::optional 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](https://gcc.godbolt.org/z/x64CVp)



### Using captures



```c++

auto result = ctre::match<"(?\\d{4})/(?\\d{1,2})/(?\\d{1,2})">(s);

return date{result.get<"year">(), result.get<"month">, result.get<"day">};



// or in C++ emulation, but the object must have a linkage

static constexpr ctll::fixed_string year = "year";

static constexpr ctll::fixed_string month = "month";

static constexpr ctll::fixed_string day = "day";

return date{result.get(), result.get, result.get};



// or use numbered access

// capture 0 is the whole match

return date{result.get<1>(), result.get<2>, result.get<3>};

```



### Lexer



```c++

enum class type {

    unknown, identifier, number

};



struct lex_item {

    type t;

    std::string_view c;

};



std::optional 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](https://gcc.godbolt.org/z/PKTiCC)



### Range over input



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



```c++

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



for (auto match: ctre::range<"([0-9]+),?">(input)) {

    std::cout << std::string_view{match.get<0>()} << "\n";

}

```



### Unicode



```c++

#include 

#include 

// needed if you want to output to the terminal

std::string_view cast_from_unicode(std::u8string_view input) noexcept {

    return std::string_view(reinterpret_cast(input.data()), input.size());

}

int main()

{

    using namespace std::literals;

    std::u8string_view original = u8"Tu es un génie"sv;



    for (auto match : ctre::range<"\\p{Letter}+">(original))

        std::cout << cast_from_unicode(match) << std::endl;

    return 0;

}

```



[link to compiler explorer](https://godbolt.org/z/erTshe6sz)



## Installing ctre using vcpkg



You can download and install ctre using the [vcpkg](https://github.com/Microsoft/vcpkg) dependency manager:



```bash

git clone https://github.com/Microsoft/vcpkg.git

cd vcpkg

./bootstrap-vcpkg.sh

./vcpkg integrate install

./vcpkg install ctre

```



The ctre port in vcpkg is kept up to date by Microsoft team members and community contributors. If the version is out of date, please [create an issue or pull request](https://github.com/Microsoft/vcpkg) on the vcpkg repository.



## Running tests (for developers)



Just run `make` in root of this project.