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117 lines
4.5 KiB
C++
117 lines
4.5 KiB
C++
// -*- C++ -*-
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/**
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* \file trivstring.h
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* This file is part of LyX, the document processor.
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* Licence details can be found in the file COPYING.
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*
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* \author Georg Baum
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*
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* Full author contact details are available in file CREDITS.
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*/
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#ifndef LYX_TRIVSTRING_H
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#define LYX_TRIVSTRING_H
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#include "support/strfwd.h"
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#ifdef STD_STRING_USES_COW
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#include <cstdlib>
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namespace lyx {
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/**
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* Trivial string class with almost no features.
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* The public interface is a subset of the std::basic_string interface.
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* The only important feature is that any read-only access does not need
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* synchronization between multiple threads, i.e. it is thread-safe without
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* locking.
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* Therefore you can safely use a const trivial_string object in multiple
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* threads at the same time. This is not the case for std::basic_string in some
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* STL implementations (e. g. GNU libcstd++, see bug 9336 and
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* https://gcc.gnu.org/bugzilla/show_bug.cgi?id=21334.
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* This class should not be used for anything else than providing thread-safety.
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* It should be removed as soon as LyX requires C++11, and all supported STL
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* implementations provide a C++11 conformant std::basic_string.
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*
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* If you change anything in this class please ensure that the unit test
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* tests/check_trivstring.cpp still tests 100% of the public interface.
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*/
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template <typename Char> class trivial_string
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{
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public:
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/// Corresponding std::basic_string
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typedef std::basic_string<Char, std::char_traits<Char>, std::allocator<Char> > _stdstring;
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/// Construct an empty string
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trivial_string() : size_(0), data_(0) {}
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/// Construct a string from a copy of \p that
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trivial_string(trivial_string const & that);
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/// Construct a string from a copy of \p that
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trivial_string(Char const * that, size_t n);
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/// Construct a string from a copy of \p that
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trivial_string(_stdstring const & that);
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///
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~trivial_string() { if (!use_sso()) delete[] data_; }
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/// Assign a copy of \p that
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trivial_string & operator=(trivial_string const & that);
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/// Assign a copy of \p that
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trivial_string & operator=(_stdstring const & that);
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/// Exchange contents with contents of \p that
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void swap(trivial_string & that);
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/// The length of the string, excluding the final 0 character
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size_t length() const { return size_; }
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/// Is this string empty?
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bool empty() const { return size_ == 0; }
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/// Is this string ordered before, at the same position or after \p other?
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int compare(trivial_string const & other) const;
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/// Return substring of length \p n starting at \p pos
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trivial_string substr(size_t pos = 0, size_t n = _stdstring::npos) const;
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/// Create a copy as std::basic_string
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operator _stdstring() const;
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/// Return a C-compatible string, terminated by a 0 character.
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/// This is never a copy and only valid for the life time of the trivial_string instance.
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Char const * c_str() const;
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/// Return character at position \p i (validity of \i is not checked)
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Char operator[](size_t i) const;
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private:
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/**
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* Whether short string optimization is used.
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* Short string optimization is a technique where no additional memory
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* needs to be allocated to store the string contents.
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* Instead, the memory which would be used to store the pointer to the
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* character buffer is reinterpreted to be a Char * buffer.
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* On most 64 bit systems and with Char == char this allows to store
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* strings of up to 7 characters without allocating additional memory.
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*/
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bool use_sso() const { return (size_ + 1) * sizeof(Char) <= sizeof(Char *); }
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/// The character storage if sso is used
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Char * data_sso() { return reinterpret_cast<Char * >(&data_); }
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/// The character storage if sso is used
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Char const * data_sso() const { return reinterpret_cast<Char const *>(&data_); }
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/// The length of the string, excluding the final 0 character
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size_t size_;
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/// The character storage
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Char * data_;
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};
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/// Comparison operator (needed for std::set etc)
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template <typename Char> bool operator<(trivial_string<Char> const & lhs, trivial_string<Char> const & rhs);
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/// Equality operator
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template <typename Char> bool operator==(trivial_string<Char> const & lhs, trivial_string<Char> const & rhs);
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template <typename Char> bool operator==(trivial_string<Char> const & lhs, Char const * rhs);
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template <typename Char> bool operator==(Char const * lhs, trivial_string<Char> const & rhs);
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/// Stream output operator
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template <typename Char>
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std::basic_ostream<Char, std::char_traits<Char> > &
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operator<<(std::basic_ostream<Char, std::char_traits<Char> > &, trivial_string<Char> const &);
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} // namespace lyx
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#else
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#include <string>
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#endif
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#endif
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