char16_t2wchar_t.hxx

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/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4; fill-column: 100 -*- */
/*
 * This file is part of the LibreOffice project.
 *
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/.
 */
 
#pragma once
 
#include <sal/config.h>
 
#include <string_view>
 
namespace o3tl
{
#if defined _WIN32
// Helpers for safe conversion between wchar_t and char16_t in MSVC
 
static_assert(sizeof(char16_t) == sizeof(wchar_t),
              "These helper functions are only applicable to implementations with 16-bit wchar_t");
 
// While other implementations define wchar_t as 32-bit integral value, and mostly use
// char-based UTF-8 string APIs, in MSVC wchar_t is (non-conformant) 16-bit, and Unicode
// support is implemented by Unicode-aware WinAPI functions taking UTF-16 LE strings,
// and also stdlib functions taking those strings.
//
// In LibreOffice, internal string representation is also UTF-16 with system endianness
// (sal_Unicode that is typedef for char16_t); so it is an important implementation concept
// to treat internal strings as directly usable by WinAPI/stdlib functions and vice versa.
// Also, it's important to use safe conversion between unrelated underlying C++ types
// used for MSVC and LibreOffice string storage without plain reinterpret_cast that brings
// risks of masking errors like casting char buffers to wchar_t/char16_t.
//
// Use these helpers for wchar_t (WSTR, WCHAR, OLESTR etc) to char16_t (sal_Unicode) string
// conversions instead of reinterpret-cast in Windows-specific code.
inline wchar_t* toW(char16_t* p) { return reinterpret_cast<wchar_t*>(p); }
inline wchar_t const* toW(char16_t const* p) { return reinterpret_cast<wchar_t const*>(p); }
inline char16_t* toU(wchar_t* p) { return reinterpret_cast<char16_t*>(p); }
inline char16_t const* toU(wchar_t const* p) { return reinterpret_cast<char16_t const*>(p); }
 
inline std::u16string_view toU(std::wstring_view v) { return { toU(v.data()), v.size() }; }
#endif
}
 
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