base/strings/string16.h - chromium/src - Git at Google

 // Copyright 2013 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_STRINGS_STRING16_H_
 #define BASE_STRINGS_STRING16_H_

 // 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 <stddef.h>
 #include <stdint.h>
 #include <stdio.h>

 #include <functional>
 #include <string>

 #include "base/base_export.h"
 #include "build/build_config.h"

 #if defined(WCHAR_T_IS_UTF16)

 // Define a macro for wrapping construction of char16 arrays and string16s from
 // a literal string. This indirection allows for an easier migration of
 // base::char16 to char16_t on platforms where WCHAR_T_IS_UTF16, as only a one
 // character change to the macro will be necessary.
 // This macro does not exist when WCHAR_T_IS_UTF32, as it is currently not
 // possible to create a char array form a literal in this case.
 // TODO(https://crbug.com/911896): Remove this macro once base::char16 is
 // char16_t on all platforms.
 #define STRING16_LITERAL(x) L##x

 namespace base {

 typedef wchar_t char16;
 typedef std::wstring string16;

 }  // namespace base

 #elif defined(WCHAR_T_IS_UTF32)

 #include <wchar.h>  // for mbstate_t

 namespace base {

 typedef uint16_t char16;

 // 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);

 // This namespace contains the implementation of base::string16 along with
 // things that need to be found via argument-dependent lookup from a
 // base::string16.
 namespace string16_internals {

 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().
   static_assert(sizeof(int_type) > sizeof(char_type),
                 "int must be larger than 16 bits wide");

   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, size_t 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 string16_internals

 typedef std::basic_string<char16,
                           base::string16_internals::string16_char_traits>
     string16;

 namespace string16_internals {

 BASE_EXPORT extern std::ostream& operator<<(std::ostream& out,
                                             const string16& str);

 // This is required by googletest to print a readable output on test failures.
 BASE_EXPORT extern void PrintTo(const string16& str, std::ostream* out);

 }  // namespace string16_internals

 }  // 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 BASE_EXPORT
     std::basic_string<base::char16,
                       base::string16_internals::string16_char_traits>;

 // Specialize std::hash for base::string16. Although the style guide forbids
 // this in general, it is necessary for consistency with WCHAR_T_IS_UTF16
 // platforms, where base::string16 is a type alias for std::wstring.
 namespace std {
 template <>
 struct hash<base::string16> {
   std::size_t operator()(const base::string16& s) const {
     std::size_t result = 0;
     for (base::char16 c : s)
       result = (result * 131) + c;
     return result;
   }
 };
 }  // namespace std

 #endif  // WCHAR_T_IS_UTF32

 #endif  // BASE_STRINGS_STRING16_H_
	// Copyright 2013 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_STRINGS_STRING16_H_
	#define BASE_STRINGS_STRING16_H_

	// 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 <stddef.h>
	#include <stdint.h>
	#include <stdio.h>

	#include <functional>
	#include <string>

	#include "base/base_export.h"
	#include "build/build_config.h"

	#if defined(WCHAR_T_IS_UTF16)

	// Define a macro for wrapping construction of char16 arrays and string16s from
	// a literal string. This indirection allows for an easier migration of
	// base::char16 to char16_t on platforms where WCHAR_T_IS_UTF16, as only a one
	// character change to the macro will be necessary.
	// This macro does not exist when WCHAR_T_IS_UTF32, as it is currently not
	// possible to create a char array form a literal in this case.
	// TODO(https://crbug.com/911896): Remove this macro once base::char16 is
	// char16_t on all platforms.
	#define STRING16_LITERAL(x) L##x

	namespace base {

	typedef wchar_t char16;
	typedef std::wstring string16;

	} // namespace base

	#elif defined(WCHAR_T_IS_UTF32)

	#include <wchar.h> // for mbstate_t

	namespace base {

	typedef uint16_t char16;

	// 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);

	// This namespace contains the implementation of base::string16 along with
	// things that need to be found via argument-dependent lookup from a
	// base::string16.
	namespace string16_internals {

	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().
	static_assert(sizeof(int_type) > sizeof(char_type),
	"int must be larger than 16 bits wide");

	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, size_t 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 string16_internals

	typedef std::basic_string<char16,
	base::string16_internals::string16_char_traits>
	string16;

	namespace string16_internals {

	BASE_EXPORT extern std::ostream& operator<<(std::ostream& out,
	const string16& str);

	// This is required by googletest to print a readable output on test failures.
	BASE_EXPORT extern void PrintTo(const string16& str, std::ostream* out);

	} // namespace string16_internals

	} // 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 BASE_EXPORT
	std::basic_string<base::char16,
	base::string16_internals::string16_char_traits>;

	// Specialize std::hash for base::string16. Although the style guide forbids
	// this in general, it is necessary for consistency with WCHAR_T_IS_UTF16
	// platforms, where base::string16 is a type alias for std::wstring.
	namespace std {
	template <>
	struct hash<base::string16> {
	std::size_t operator()(const base::string16& s) const {
	std::size_t result = 0;
	for (base::char16 c : s)
	result = (result * 131) + c;
	return result;
	}
	};
	} // namespace std

	#endif // WCHAR_T_IS_UTF32

	#endif // BASE_STRINGS_STRING16_H_