summaryrefslogtreecommitdiff
path: root/base/string16.h
diff options
context:
space:
mode:
Diffstat (limited to 'base/string16.h')
-rw-r--r--base/string16.h178
1 files changed, 178 insertions, 0 deletions
diff --git a/base/string16.h b/base/string16.h
new file mode 100644
index 0000000..4c7b21f
--- /dev/null
+++ b/base/string16.h
@@ -0,0 +1,178 @@
+// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef BASE_STRING16_H_
+#define BASE_STRING16_H_
+#pragma once
+
+// WHAT:
+// A version of std::basic_string that provides 2-byte characters even when
+// wchar_t is not implemented as a 2-byte type. You can access this class as
+// string16. We also define char16, which string16 is based upon.
+//
+// WHY:
+// On Windows, wchar_t is 2 bytes, and it can conveniently handle UTF-16/UCS-2
+// data. Plenty of existing code operates on strings encoded as UTF-16.
+//
+// On many other platforms, sizeof(wchar_t) is 4 bytes by default. We can make
+// it 2 bytes by using the GCC flag -fshort-wchar. But then std::wstring fails
+// at run time, because it calls some functions (like wcslen) that come from
+// the system's native C library -- which was built with a 4-byte wchar_t!
+// It's wasteful to use 4-byte wchar_t strings to carry UTF-16 data, and it's
+// entirely improper on those systems where the encoding of wchar_t is defined
+// as UTF-32.
+//
+// Here, we define string16, which is similar to std::wstring but replaces all
+// libc functions with custom, 2-byte-char compatible routines. It is capable
+// of carrying UTF-16-encoded data.
+
+#include <stdio.h>
+#include <string>
+
+#include "base/base_export.h"
+#include "base/basictypes.h"
+
+#if defined(WCHAR_T_IS_UTF16)
+
+typedef wchar_t char16;
+typedef std::wstring string16;
+
+#elif defined(WCHAR_T_IS_UTF32)
+
+typedef uint16 char16;
+
+namespace base {
+
+// char16 versions of the functions required by string16_char_traits; these
+// are based on the wide character functions of similar names ("w" or "wcs"
+// instead of "c16").
+BASE_EXPORT int c16memcmp(const char16* s1, const char16* s2, size_t n);
+BASE_EXPORT size_t c16len(const char16* s);
+BASE_EXPORT const char16* c16memchr(const char16* s, char16 c, size_t n);
+BASE_EXPORT char16* c16memmove(char16* s1, const char16* s2, size_t n);
+BASE_EXPORT char16* c16memcpy(char16* s1, const char16* s2, size_t n);
+BASE_EXPORT char16* c16memset(char16* s, char16 c, size_t n);
+
+struct string16_char_traits {
+ typedef char16 char_type;
+ typedef int int_type;
+
+ // int_type needs to be able to hold each possible value of char_type, and in
+ // addition, the distinct value of eof().
+ COMPILE_ASSERT(sizeof(int_type) > sizeof(char_type), unexpected_type_width);
+
+ typedef std::streamoff off_type;
+ typedef mbstate_t state_type;
+ typedef std::fpos<state_type> pos_type;
+
+ static void assign(char_type& c1, const char_type& c2) {
+ c1 = c2;
+ }
+
+ static bool eq(const char_type& c1, const char_type& c2) {
+ return c1 == c2;
+ }
+ static bool lt(const char_type& c1, const char_type& c2) {
+ return c1 < c2;
+ }
+
+ static int compare(const char_type* s1, const char_type* s2, size_t n) {
+ return c16memcmp(s1, s2, n);
+ }
+
+ static size_t length(const char_type* s) {
+ return c16len(s);
+ }
+
+ static const char_type* find(const char_type* s, size_t n,
+ const char_type& a) {
+ return c16memchr(s, a, n);
+ }
+
+ static char_type* move(char_type* s1, const char_type* s2, int_type n) {
+ return c16memmove(s1, s2, n);
+ }
+
+ static char_type* copy(char_type* s1, const char_type* s2, size_t n) {
+ return c16memcpy(s1, s2, n);
+ }
+
+ static char_type* assign(char_type* s, size_t n, char_type a) {
+ return c16memset(s, a, n);
+ }
+
+ static int_type not_eof(const int_type& c) {
+ return eq_int_type(c, eof()) ? 0 : c;
+ }
+
+ static char_type to_char_type(const int_type& c) {
+ return char_type(c);
+ }
+
+ static int_type to_int_type(const char_type& c) {
+ return int_type(c);
+ }
+
+ static bool eq_int_type(const int_type& c1, const int_type& c2) {
+ return c1 == c2;
+ }
+
+ static int_type eof() {
+ return static_cast<int_type>(EOF);
+ }
+};
+
+} // namespace base
+
+// The string class will be explicitly instantiated only once, in string16.cc.
+//
+// std::basic_string<> in GNU libstdc++ contains a static data member,
+// _S_empty_rep_storage, to represent empty strings. When an operation such
+// as assignment or destruction is performed on a string, causing its existing
+// data member to be invalidated, it must not be freed if this static data
+// member is being used. Otherwise, it counts as an attempt to free static
+// (and not allocated) data, which is a memory error.
+//
+// Generally, due to C++ template magic, _S_empty_rep_storage will be marked
+// as a coalesced symbol, meaning that the linker will combine multiple
+// instances into a single one when generating output.
+//
+// If a string class is used by multiple shared libraries, a problem occurs.
+// Each library will get its own copy of _S_empty_rep_storage. When strings
+// are passed across a library boundary for alteration or destruction, memory
+// errors will result. GNU libstdc++ contains a configuration option,
+// --enable-fully-dynamic-string (_GLIBCXX_FULLY_DYNAMIC_STRING), which
+// disables the static data member optimization, but it's a good optimization
+// and non-STL code is generally at the mercy of the system's STL
+// configuration. Fully-dynamic strings are not the default for GNU libstdc++
+// libstdc++ itself or for the libstdc++ installations on the systems we care
+// about, such as Mac OS X and relevant flavors of Linux.
+//
+// See also http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24196 .
+//
+// To avoid problems, string classes need to be explicitly instantiated only
+// once, in exactly one library. All other string users see it via an "extern"
+// declaration. This is precisely how GNU libstdc++ handles
+// std::basic_string<char> (string) and std::basic_string<wchar_t> (wstring).
+//
+// This also works around a Mac OS X linker bug in ld64-85.2.1 (Xcode 3.1.2),
+// in which the linker does not fully coalesce symbols when dead code
+// stripping is enabled. This bug causes the memory errors described above
+// to occur even when a std::basic_string<> does not cross shared library
+// boundaries, such as in statically-linked executables.
+//
+// TODO(mark): File this bug with Apple and update this note with a bug number.
+
+extern template class std::basic_string<char16, base::string16_char_traits>;
+
+typedef std::basic_string<char16, base::string16_char_traits> string16;
+
+namespace base {
+BASE_EXPORT extern std::ostream& operator<<(std::ostream& out,
+ const string16& str);
+}
+
+#endif // WCHAR_T_IS_UTF32
+
+#endif // BASE_STRING16_H_