4 * This file is part of LyX, the document processor.
5 * Licence details can be found in the file COPYING.
9 * Full author contact details are available in file CREDITS.
12 #ifndef LYX_TRIVSTRING_H
13 #define LYX_TRIVSTRING_H
15 #include "support/strfwd.h"
22 * Trivial string class with almost no features.
23 * The public interface is a subset of the std::basic_string interface.
24 * The only important feature is that any read-only access does not need
25 * synchronization between multiple threads, i.e. it is thread-safe without
27 * Therefore you can safely use a const trivial_string object in multiple
28 * threads at the same time. This is not the case for std::basic_string in some
29 * STL implementations (e. g. GNU libcstd++, see bug 9336 and
30 * https://gcc.gnu.org/bugzilla/show_bug.cgi?id=21334.
31 * This class should not be used for anything else than providing thread-safety.
32 * It should be removed as soon as LyX requires C++11, and all supported STL
33 * implementations provide a C++11 conformant std::basic_string.
35 template <typename Char> class trivial_string
38 /// Construct an empty string
39 trivial_string() : size_(0), data_(0) {}
40 /// Construct a string from a copy of \p that
41 trivial_string(trivial_string const & that);
42 /// Construct a string from a copy of \p that
43 trivial_string(std::basic_string<Char, std::char_traits<Char>, std::allocator<Char> > const & that);
45 ~trivial_string() { if (!use_sso()) delete[] data_; }
46 /// Assign a copy of \p that
47 trivial_string & operator=(trivial_string const & that);
48 /// Assign a copy of \p that
49 trivial_string & operator=(std::basic_string<Char, std::char_traits<Char>, std::allocator<Char> > const & that);
50 /// Exchange contents with contents of \p that
51 void swap(trivial_string & that);
52 /// The length of the string, excluding the final 0 character
53 size_t length() const { return size_; }
54 /// Is this string empty?
55 bool empty() const { return size_ == 0; }
56 /// Is this string ordered before, at the same position or after \p other?
57 int compare(trivial_string const & other) const;
58 /// Create a copy as std::basic_string
59 std::basic_string<Char, std::char_traits<Char>, std::allocator<Char> > str() const;
60 /// Return a C-compatible string, terminated by a 0 character.
61 /// This is never a copy and only valid for the life time of the trivial_string instance.
62 Char const * c_str() const;
65 * Whether short string optimization is used.
66 * Short string optimization is a technique where no additional memory
67 * needs to be allocated to store the string contents.
68 * Instead, the memory which would be used to store the pointer to the
69 * character buffer is reinterpreted to be a Char * buffer.
70 * On most 64 bit systems and with Char == char this allows to store
71 * strings of up to 7 characters without allocating additional memory.
73 bool use_sso() const { return (size_ + 1) * sizeof(Char) <= sizeof(Char *); }
74 /// The character storage if sso is used
75 Char * data_sso() { return reinterpret_cast<Char * >(&data_); }
76 /// The character storage if sso is used
77 Char const * data_sso() const { return reinterpret_cast<Char const *>(&data_); }
78 /// The length of the string, excluding the final 0 character
80 /// The character storage
83 template <typename Char> bool operator<(trivial_string<Char> const & lhs, trivial_string<Char> const &rhs);