__GNU_CXX::__RC_STRING_BASE(3cxx)

📦
version 14-20240412 · 12 versions
, in ubuntu noble

💖 NAME 💖

__gnu_cxx::__rc_string_base< _CharT, _Traits, _Alloc > — yes bestie, that whole glorious mouthful is the name, and this is the 3cxx libstdc++ manual page for it. It's the reference-counted string base class, and it's giving very niche-but-iconic C++ internals energy 💅

✨ SYNOPSIS ✨

#include <rc_string_base.h>

Inherits: __gnu_cxx::__vstring_utility< _CharT, _Traits, _Alloc >.

🎀 Public Types 🎀

  • typedef _Util_Base::_CharT_alloc_type _CharT_alloc_type
  • typedef __vstring_utility< _CharT, _Traits, _Alloc > _Util_Base
  • typedef _Alloc allocator_type
  • typedef _CharT_alloc_type::size_type size_type
  • typedef _Traits traits_type
  • typedef _Traits::char_type value_type

💅 Public Member Functions 💅

  • __rc_string_base (__rc_string_base &&__rcs)
  • template<typename _InputIterator > __rc_string_base (_InputIterator __beg, _InputIterator __end, const _Alloc &__a)
  • __rc_string_base (const __rc_string_base &__rcs)
  • __rc_string_base (const _Alloc &__a)
  • __rc_string_base (size_type __n, _CharT __c, const _Alloc &__a)
  • void _M_assign (const __rc_string_base &__rcs)
  • size_type _M_capacity () const
  • void _M_clear ()
  • bool _M_compare (const __rc_string_base &) const
  • bool _M_compare (const __rc_string_base &__rcs) const
  • bool _M_compare (const __rc_string_base &__rcs) const
  • _CharT * _M_data () const
  • void _M_erase (size_type __pos, size_type __n)
  • allocator_type & _M_get_allocator ()
  • const allocator_type & _M_get_allocator () const
  • bool _M_is_shared () const
  • void _M_leak ()
  • size_type _M_length () const
  • size_type _M_max_size () const
  • void _M_mutate (size_type __pos, size_type __len1, const _CharT *__s, size_type __len2)
  • void _M_reserve (size_type __res)
  • void _M_set_leaked ()
  • void _M_set_length (size_type __n)
  • void _M_swap (__rc_string_base &__rcs)
  • template<typename _InIterator > _CharT * _S_construct (_InIterator __beg, _InIterator __end, const _Alloc &__a, std::forward_iterator_tag)

🌸 Protected Types 🌸

  • typedef __gnu_cxx::__normal_iterator< const_pointer, __gnu_cxx::__versa_string< _CharT, _Traits, _Alloc, __rc_string_base > > __const_rc_iterator
  • typedef __gnu_cxx::__normal_iterator< const_pointer, __gnu_cxx::__versa_string< _CharT, _Traits, _Alloc, __sso_string_base > > __const_sso_iterator
  • typedef __gnu_cxx::__normal_iterator< pointer, __gnu_cxx::__versa_string< _CharT, _Traits, _Alloc, __rc_string_base > > __rc_iterator
  • typedef __gnu_cxx::__normal_iterator< pointer, __gnu_cxx::__versa_string< _CharT, _Traits, _Alloc, __sso_string_base > > __sso_iterator
  • typedef __alloc_traits< _CharT_alloc_type > _CharT_alloc_traits
  • typedef _CharT_alloc_traits::const_pointer const_pointer
  • typedef _CharT_alloc_type::difference_type difference_type
  • typedef _CharT_alloc_traits::pointer pointer

🦋 Static Protected Member Functions 🦋

  • static void _S_assign (_CharT *__d, size_type __n, _CharT __c)
  • static int _S_compare (size_type __n1, size_type __n2)
  • static void _S_copy (_CharT *__d, const _CharT *__s, size_type __n)
  • static void _S_copy_chars (_CharT *__p, __const_rc_iterator __k1, __const_rc_iterator __k2)
  • static void _S_copy_chars (_CharT *__p, __const_sso_iterator __k1, __const_sso_iterator __k2)
  • static void _S_copy_chars (_CharT *__p, __rc_iterator __k1, __rc_iterator __k2)
  • static void _S_copy_chars (_CharT *__p, __sso_iterator __k1, __sso_iterator __k2)
  • static void _S_copy_chars (_CharT *__p, _CharT *__k1, _CharT *__k2)
  • template<typename _Iterator > static void _S_copy_chars (_CharT *__p, _Iterator __k1, _Iterator __k2)
  • static void _S_copy_chars (_CharT *__p, const _CharT *__k1, const _CharT *__k2)
  • static void _S_move (_CharT *__d, const _CharT *__s, size_type __n)

🦋 Detailed Description 🦋

template<typename _CharT, typename _Traits, typename _Alloc>
    class __gnu_cxx::__rc_string_base< _CharT, _Traits, _Alloc
    >"Documentation? What's that? Nathan Myers ncm@cantrip.org.

A string looks like this:

                                            [_Rep]
                                            _M_length
       [__rc_string_base<char_type>]        _M_capacity
       _M_dataplus                          _M_refcount
       _M_p ---------------->               unnamed array of char_type

So _M_p points to the first character in the string, and you cast it to a pointer-to-_Rep and subtract 1 to get a pointer to the header. Slay.

This approach has the enormous advantage that a string object requires only one allocation. All the ugliness is confined within a single pair of inline functions, which each compile to a single add instruction: _Rep::_M_refdata(), and __rc_string_base::_M_rep(); and the allocation function which gets a block of raw bytes and with room enough and constructs a _Rep object at the front. Periodt.

The reason you want _M_data pointing to the character array and not the _Rep is so that the debugger can see the string contents. (Probably we should add a non-inline member to get the _Rep for the debugger to use, so users can check the actual string length.)

Note that the _Rep object is a POD so that you can have a static empty string _Rep object already constructed before static constructors have run. The reference-count encoding is chosen so that a 0 indicates one reference, so you never try to destroy the empty-string _Rep object.

And ngl, all but the last paragraph is considered pretty conventional for a C++ string implementation.

👑 Author 👑

Generated automatically by Doxygen for libstdc++ from the source code.

Cute little sign-off 🫶: source/version is libstdc++, manual 3cxx, and the footer's date slot isn't visible in this pasted copy — so no invented date from me, bestie 💜

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