Boost C++ Libraries

boost/process/v2/cstring_ref.hpp

// Copyright (c) 2022 Klemens D. Morgenstern
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
#ifndef BOOST_PROCESS_V2_CSTRING_REF_HPP
#define BOOST_PROCESS_V2_CSTRING_REF_HPP

#include <boost/process/v2/detail/config.hpp>

#if defined(BOOST_PROCESS_V2_STANDALONE)
#include <string_view>
#else
#include <boost/utility/string_view.hpp>
#endif

BOOST_PROCESS_V2_BEGIN_NAMESPACE

namespace detail
{

BOOST_CONSTEXPR static const char*     null_char_(char)     {return "";}
BOOST_CONSTEXPR static const wchar_t*  null_char_(wchar_t)  {return L"";}
BOOST_CONSTEXPR static const char16_t* null_char_(char16_t) {return u"";}
BOOST_CONSTEXPR static const char32_t* null_char_(char32_t) {return U"";}

#if defined(BOOST_PROCESS_V2_HAS_CHAR8_T)
BOOST_CONSTEXPR static const char8_t* null_char_(char8_t) {return u8"";}
#endif

}

#if defined(BOOST_PROCESS_V2_STANDALONE)
using std::basic_string_view;
using std::   string_view;
using std::  wstring_view;
#else
using boost::basic_string_view;
using boost::   string_view;
using boost::  wstring_view;
#endif


/// Small wrapper for a null-terminated string that can be directly passed to C APIS
/** This ref can only be modified by moving the front pointer. It does not store the 
 * size, but can detect values that can directly be passed to system APIs.
 * 
 * It can be constructed from a `char*` pointer or any class that has a `c_str()` 
 * member function, e.g. std::string or boost::static_string.
 * 
 */
template<typename CharT, typename Traits = std::char_traits<CharT>>
struct basic_cstring_ref
{
    using value_type             = CharT;
    using traits_type            = Traits;

    BOOST_CONSTEXPR basic_cstring_ref() noexcept : view_(detail::null_char_(value_type{})) {}
    BOOST_CONSTEXPR basic_cstring_ref(std::nullptr_t) = delete;

    BOOST_CONSTEXPR basic_cstring_ref( const value_type* s ) : view_(s) {}

    template<typename Source,
            typename =
            typename std::enable_if<
                    std::is_same<const value_type,
                            typename std::remove_pointer<decltype(std::declval<Source>().c_str())>::type
                    >::value>::type>
    BOOST_CONSTEXPR basic_cstring_ref(Source && src) : view_(src.c_str()) {}

    BOOST_CONSTEXPR typename basic_string_view<value_type, Traits>::const_pointer c_str() const BOOST_NOEXCEPT
    {
        return this->data();
    }

    using string_view_type = basic_string_view<value_type, Traits>;
    constexpr operator string_view_type() const {return view_;}

    using pointer                =       CharT *;
    using const_pointer          = const CharT *;
    using reference              =       CharT &;
    using const_reference        = const CharT &;
    using const_iterator         = const_pointer;
    using iterator               = const_iterator;
    using const_reverse_iterator = typename std::reverse_iterator<const_iterator>;
    using reverse_iterator       = typename std::reverse_iterator<iterator>;
    using size_type              = std::size_t;
    using difference_type        = std::ptrdiff_t;

    static BOOST_CONSTEXPR size_type npos = -1;

    BOOST_CONSTEXPR const_iterator begin()  const BOOST_NOEXCEPT {return view_;};
    BOOST_CONSTEXPR const_iterator end()    const BOOST_NOEXCEPT {return view_ + length();};
    BOOST_CONSTEXPR const_iterator cbegin() const BOOST_NOEXCEPT {return view_;};
    BOOST_CONSTEXPR const_iterator cend()   const BOOST_NOEXCEPT {return view_ + length();};
    BOOST_CONSTEXPR const_reverse_iterator rbegin()  const BOOST_NOEXCEPT {return reverse_iterator(view_ + length());};
    BOOST_CONSTEXPR const_reverse_iterator rend()    const BOOST_NOEXCEPT {return reverse_iterator(view_);};
    BOOST_CONSTEXPR const_reverse_iterator crbegin() const BOOST_NOEXCEPT {return reverse_iterator(view_ + length());};
    BOOST_CONSTEXPR const_reverse_iterator crend()   const BOOST_NOEXCEPT {return reverse_iterator(view_);};

    BOOST_CONSTEXPR size_type size() const BOOST_NOEXCEPT {return length(); }
    BOOST_CONSTEXPR size_type length() const BOOST_NOEXCEPT {return traits_type::length(view_); }
    BOOST_CONSTEXPR size_type max_size() const BOOST_NOEXCEPT {return (std::numeric_limits<std::size_t>::max)() / sizeof(CharT); }
    BOOST_ATTRIBUTE_NODISCARD BOOST_CONSTEXPR bool empty() const BOOST_NOEXCEPT {return *view_ == *detail::null_char_(CharT{}); }

    BOOST_CONSTEXPR const_reference operator[](size_type pos) const  {return view_[pos] ;}
    BOOST_CXX14_CONSTEXPR const_reference at(size_type pos) const
    {
        if (pos >= size())
            throw_exception(std::out_of_range("cstring-view out of range"));
        return view_[pos];
    }
    BOOST_CONSTEXPR const_reference front() const  {return *view_;}
    BOOST_CONSTEXPR const_reference back()  const  {return view_[length() - 1];}
    BOOST_CONSTEXPR const_pointer data()    const BOOST_NOEXCEPT  {return view_;}
    BOOST_CXX14_CONSTEXPR void remove_prefix(size_type n)  {view_ = view_ + n;}
    void swap(basic_cstring_ref& s) BOOST_NOEXCEPT {std::swap(view_, s.view_);}

    size_type copy(value_type* s, size_type n, size_type pos = 0) const
    {
        return traits_type::copy(s, view_ + pos, n) - view_;
    }
    BOOST_CONSTEXPR basic_cstring_ref substr(size_type pos = 0) const
    {
        return basic_cstring_ref(view_ + pos);
    }

    BOOST_CONSTEXPR string_view_type substr(size_type pos, size_type length) const
    {
        return string_view_type(view_).substr(pos, length);
    }

    BOOST_CXX14_CONSTEXPR int compare(basic_cstring_ref x) const BOOST_NOEXCEPT
    {
        auto idx = 0u;
        for (; view_[idx] != null_char_()[0] && x[idx] != null_char_()[0]; idx++)
            if (!traits_type::eq(view_[idx], x[idx]))
                return traits_type::lt(view_[idx], x[idx]) ? -1 : 1;

        return traits_type::to_int_type(view_[idx]) -
               traits_type::to_int_type(x[idx]); // will compare to null char of either.
    }

    BOOST_CXX14_CONSTEXPR bool starts_with(string_view_type x) const BOOST_NOEXCEPT
    {
        if (x.empty())
            return true;

        auto idx = 0u;
        for (; view_[idx] != null_char_()[0] && idx < x.size(); idx++)
            if (!traits_type::eq(view_[idx], x[idx]))
                return false;

        return idx == x.size() || view_[idx] != null_char_()[0];
    }
    BOOST_CONSTEXPR bool starts_with(value_type x)       const BOOST_NOEXCEPT
    {
        return traits_type::eq(view_[0], x);
    }

    BOOST_CXX14_CONSTEXPR size_type find( CharT ch, size_type pos = 0 ) const BOOST_NOEXCEPT
    {
        for (auto p = view_ + pos; *p != *null_char_(); p++)
            if (traits_type::eq(*p, ch))
                return p - view_;
        return npos;
    }


    friend BOOST_CXX14_CONSTEXPR bool operator==(basic_cstring_ref x, basic_cstring_ref y) BOOST_NOEXCEPT
    {
        std::size_t idx = 0u;
        for (idx = 0u; x[idx] != null_char_()[0] && y[idx] != null_char_()[0]; idx++)
            if (!traits_type::eq(x[idx], y[idx]))
                return false;
        return x[idx] == y[idx];
    }
    friend BOOST_CXX14_CONSTEXPR bool operator!=(basic_cstring_ref x, basic_cstring_ref y) BOOST_NOEXCEPT
    {
        std::size_t idx = 0u;
        for (idx = 0u; x[idx] != null_char_()[0] &&
                       y[idx] != null_char_()[0]; idx++)
            if (!traits_type::eq(x[idx], y[idx]))
                return true;
        return x[idx] != y[idx];
    }
    friend BOOST_CXX14_CONSTEXPR bool operator< (basic_cstring_ref x, basic_cstring_ref y) BOOST_NOEXCEPT {return x.compare(y) <  0;}
    friend BOOST_CXX14_CONSTEXPR bool operator> (basic_cstring_ref x, basic_cstring_ref y) BOOST_NOEXCEPT {return x.compare(y) >  0;}
    friend BOOST_CXX14_CONSTEXPR bool operator<=(basic_cstring_ref x, basic_cstring_ref y) BOOST_NOEXCEPT {return x.compare(y) <= 0;}
    friend BOOST_CXX14_CONSTEXPR bool operator>=(basic_cstring_ref x, basic_cstring_ref y) BOOST_NOEXCEPT {return x.compare(y) >= 0;}

    // modifiers
    void clear() BOOST_NOEXCEPT { view_ =  null_char_(); }          // Boost extension

    std::basic_string<value_type, traits_type> to_string() const {
        return std::basic_string<CharT, Traits>(begin(), end());
    }

    template<typename Allocator>
    std::basic_string<value_type, traits_type, Allocator> to_string(const Allocator& a) const {
        return std::basic_string<value_type, traits_type, Allocator>(begin(), end(), a);
    }

  private:
    BOOST_CONSTEXPR static const_pointer   null_char_()         {return detail::null_char_(CharT{});}
    const_pointer view_;
};

template<class charT, class traits>
inline std::basic_ostream<charT, traits>&
operator<<(std::basic_ostream<charT, traits>& os,
           const basic_cstring_ref<charT,traits>& str)
{
    return os << static_cast<basic_string_view<charT, traits>>(str);
}

template <class charT, class traits>
std::size_t hash_value(basic_string_view<charT, traits> s) {
    return boost::hash_range(s.begin(), s.end());
}

using cstring_ref    = basic_cstring_ref<char>;
using wcstring_ref   = basic_cstring_ref<wchar_t>;
using u16cstring_ref = basic_cstring_ref<char16_t>;
using u32cstring_ref = basic_cstring_ref<char32_t>;

#if defined(BOOST_PROCESS_V2_HAS_CHAR8_T)
using u8cstring_ref  = basic_cstring_ref<char8_t>;
#endif

BOOST_PROCESS_V2_END_NAMESPACE

#endif //BOOST_PROCESS_V2_CSTRING_REF_HPP