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  "contentMarkdown": "# Windows C++ 中的 `LPCTSTR`、Unicode 与字符串转换\n\n## 类型关系\n\n`LPCTSTR` 是 Windows 头文件中的历史兼容别名：\n\n- 定义 `UNICODE` 时，`LPCTSTR` 等价于 `const wchar_t*`。\n- 未定义 `UNICODE` 时，`LPCTSTR` 等价于 `const char*`。\n- `LPCWSTR` 始终是 `const wchar_t*`；`LPCSTR` 始终是 `const char*`。\n\n新 Windows 项目通常直接使用 Unicode 版本的 API（名称以 `W` 结尾）和明确的 `wchar_t`/UTF-16 类型，避免让同一源代码因宏配置不同而改变字符类型。\n\n## `L` 前缀不是“转换”\n\n```cpp\nconst wchar_t* text = L\"hello\";\n```\n\n`L\"hello\"` 在编译期创建宽字符串字面量；它不是把运行时的窄字符串转换成宽字符串。Windows 上的 `wchar_t` 通常是 16 位，API 的宽字符串采用 UTF-16 编码单元。一个 Unicode 码点不一定只占一个 `wchar_t`，补充平面字符需要代理项对。\n\n## 运行时转换\n\n在 Windows API 边界，使用 `MultiByteToWideChar` 和 `WideCharToMultiByte`，并明确窄字符串的编码：\n\n```cpp\n#include <windows.h>\n#include <string>\n#include <stdexcept>\n\nstd::wstring Utf8ToWide(const std::string& input) {\n    if (input.empty()) return {};\n\n    int count = MultiByteToWideChar(\n        CP_UTF8, MB_ERR_INVALID_CHARS,\n        input.data(), static_cast<int>(input.size()),\n        nullptr, 0);\n    if (count == 0) throw std::runtime_error(\"invalid UTF-8\");\n\n    std::wstring output(count, L'\\0');\n    MultiByteToWideChar(\n        CP_UTF8, MB_ERR_INVALID_CHARS,\n        input.data(), static_cast<int>(input.size()),\n        output.data(), count);\n    return output;\n}\n```\n\n不要依赖系统当前代码页把 UTF-8 当作本地 ANSI 编码；也不要使用简单强制转换在 `char*` 与 `wchar_t*` 之间重解释内存。\n\n## `TCHAR` 与 `_T()`\n\n`TCHAR`、`LPCTSTR`、`TEXT()`/`_T()` 用于早期同时构建 ANSI 和 Unicode 版本的代码。维护遗留项目时需要理解它们；新代码若只支持现代 Windows，可统一启用 Unicode，并在模块边界明确 UTF-8 与 UTF-16 的转换。\n\n## 参考资料\n\n- [Microsoft Learn：Working with Strings](https://learn.microsoft.com/en-us/windows/win32/learnwin32/working-with-strings)\n- [Microsoft Learn：String and Character Literals](https://learn.microsoft.com/en-us/cpp/cpp/string-and-character-literals-cpp?view=msvc-170)\n"
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