错误C2664:无法转换参数错误

错误是自称的。您正在通过wchar_t缓冲区/指针，其中预期char*指针。它们不是兼容类型。请注意，所有错误消息都指出了API函数的A NSI版本。

请勿使用#undef UNICODE！（联合）定义UNICODE（和C RTL的_UNICODE）并不是代码的责任。调用编译器时要处理该项目的责任。

通过不确定的UNICODE手动，您强迫所有基于TCHAR的Win32 API宏（就像您正在呼叫的API宏一样）将映射到ANSI版本而不是Unicode版本。

如果要使用ANSI字符串，请明确调用A NSI功能。如果要使用Unicode字符串，请明确调用W IDE功能。停止依靠TCHAR定义。

而是尝试一下：

NativeLibrary LoadNativeLibraryHelper(const std::string& library_path,
                                      LoadLibraryFunction load_library_api,
                                      NativeLibraryLoadError* error) {
  // LoadLibrary() opens the file off disk.
  //ThreadRestrictions::AssertIOAllowed();
  // Switch the current directory to the library directory as the library
  // may have dependencies on DLLs in this directory.
  WCHAR current_directory[MAX_PATH] = {0};
  bool restore_directory = false;
  // THIS IS NOT THE PROPER WAY TO CONVERT A std::string TO A std::wstring!
  // This only works properly for ASCII strings.  You need to use
  // MultiByteToWideChar() or std::wstring_convert or other equivalent
  // to convert ANSI data to UNICODE data.  Otherwise, library_path should
  // be passed as a std::wstring to begin with...
  //
  std::wstring lp = std::wstring(library_path.begin(), library_path.end());
  std::wstring plugin_path, plugin_value;    
  const wchar_t *res = wcsrchr(lp.c_str(), L'');
  if (res)
  {
    plugin_path.assign(lp.c_str(), res);
    plugin_value.assign(++res);
    if (!plugin_path.empty())
    {
      GetCurrentDirectoryW(MAX_PATH, current_directory);
      restore_directory = SetCurrentDirectoryW(plugin_path.c_str());
    }
  }
  else
    plugin_value = lp;
  HMODULE module = (*load_library_api)(plugin_value.c_str());
  if (!module && error) {
    // GetLastError() needs to be called immediately after |load_library_api|.
    error->code = GetLastError();
  }
  if (restore_directory)
    SetCurrentDirectoryW(current_directory);
  return module;
}
...
NativeLibrary LoadNativeLibraryDynamically(const std::string& library_path) {
  LoadLibraryFunction load_library;
  load_library = reinterpret_cast<LoadLibraryFunction>(
      GetProcAddress(GetModuleHandleW(L"kernel32.dll"), "LoadLibraryW"));
  return LoadNativeLibraryHelper(library_path, load_library, NULL);
}

话虽如此，请勿使用SetCurrentDirectory()影响搜索依赖的DLL的位置！正确的解决方案是使用SetDllDirectory()（XP SP1 ）或AddDllDirectory()（Win8 ）。

仅使用SetDllDirectory()：

NativeLibrary LoadNativeLibraryHelper(const std::string& library_path,
                                      LoadLibraryFunction load_library_api,
                                      NativeLibraryLoadError* error) {
  // LoadLibrary() opens the file off disk.
  //ThreadRestrictions::AssertIOAllowed();
  // Include the library directory as the library may have dependencies on
  // DLLs in this directory.
  // THIS IS NOT THE PROPER WAY TO CONVERT A std::string TO A std::wstring!
  // This only works properly for ASCII strings.  You need to use
  // MultiByteToWideChar() or std::wstring_convert or other equivalent
  // to convert ANSI data to UNICODE data.  Otherwise, library_path should
  // be passed as a std::wstring to begin with...
  //
  std::wstring lp = std::wstring(library_path.begin(), library_path.end());
  std::wstring plugin_path, plugin_value;
  bool restore_old_order = false;
  const wchar_t *res = wcsrchr(lp.c_str(), L'');
  if (res)
  {
    plugin_path.assign(lp.c_str(), res);
    plugin_value.assign(++res);
    if (!plugin_path.empty())
      restore_old_order = SetDllDirectoryW(plugin_path.c_str());
  }
  else
    plugin_value = lp;
  HMODULE module = (*load_library_api)(plugin_value.c_str());
  if (!module && error) {
    // GetLastError() needs to be called immediately after |load_library_api|.
    error->code = GetLastError();
  }
  if (restore_old_order)
      SetDllDirectoryW(NULL);
  return module;
}

仅使用AddDllDirectory()：

NativeLibrary LoadNativeLibraryHelper(const std::string& library_path,
                                      LoadLibraryFunction load_library_api,
                                      NativeLibraryLoadError* error) {
  // LoadLibrary() opens the file off disk.
  //ThreadRestrictions::AssertIOAllowed();
  // Include the library directory as the library may have dependencies on
  // DLLs in this directory.
  // THIS IS NOT THE PROPER WAY TO CONVERT A std::string TO A std::wstring!
  // This only works properly for ASCII strings.  You need to use
  // MultiByteToWideChar() or std::wstring_convert or other equivalent
  // to convert ANSI data to UNICODE data.  Otherwise, library_path should
  // be passed as a std::wstring to begin with...
  //
  std::wstring lp = std::wstring(library_path.begin(), library_path.end());
  std::wstring plugin_path, plugin_value;
  DLL_DIRECTORY_COOKIE cookie = 0;
  const wchar_t *res = wcsrchr(lp.c_str(), L'');
  if (res)
  {
    plugin_path.assign(lp.c_str(), res);
    plugin_value.assign(++res);
    if (!plugin_path.empty())
      cookie = AddDllDirectory(plugin_path.c_str());
  }
  else
    plugin_value = lp;
  HMODULE module = (*load_library_api)(plugin_value.c_str());
  if (!module && error) {
    // GetLastError() needs to be called immediately after |load_library_api|.
    error->code = GetLastError();
  }
  if (cookie)
    RemoveDllDirectory(cookie);
  return module;
}

使用在运行时实际可用的任何一个：

NativeLibrary LoadNativeLibraryHelper(const std::string& library_path,
                                      LoadLibraryFunction load_library_api,
                                      NativeLibraryLoadError* error) {
  // LoadLibrary() opens the file off disk.
  //ThreadRestrictions::AssertIOAllowed();
  // Include the library directory as the library may have dependencies on
  // DLLs in this directory.
  typedef BOOL (WINAPI* SetDllDirectoryFunction)(LPCWSTR lpPathName);
  typedef PVOID DLL_DIRECTORY_COOKIE;
  typedef DLL_DIRECTORY_COOKIE (WINAPI* AddDllDirectoryFunction)(PCWSTR NewDirectory);
  typedef BOOL(WINAPI* RemoveDllDirectoryFunction)(DLL_DIRECTORY_COOKIE Cookie);
  HMODULE hKernel32 = GetModuleHandleW(L"kernel32.dll");
  AddDllDirectoryFunction add_dll_directory;
  add_dll_directory = reinterpret_cast<AddDllDirectoryFunction>(
    GetProcAddress(hKernel32, "AddDllDirectory"));
  RemoveDllDirectoryFunction remove_dll_directory;
  if (add_dll_directory)
  {
    remove_dll_directory = reinterpret_cast<RemoveDllDirectoryFunction>(
      GetProcAddress(hKernel32, "RemoveDllDirectory"));
  }
  else
    remove_dll_directory = NULL;
  SetDllDirectoryFunction set_dll_directory;
  if (!(add_dll_directory && remove_dll_directory))
  {
    set_dll_directory = reinterpret_cast<SetDllDirectoryFunction>(
      GetProcAddress(hKernel32, "SetDllDirectoryW"));
  }
  else
    set_dll_directory = NULL;
  // THIS IS NOT THE PROPER WAY TO CONVERT A std::string TO A std::wstring!
  // This only works properly for ASCII strings.  You need to use
  // MultiByteToWideChar() or std::wstring_convert or other equivalent
  // to convert ANSI data to UNICODE data.  Otherwise, library_path should
  // be passed as a std::wstring to begin with...
  //
  std::wstring lp = std::wstring(library_path.begin(), library_path.end());
  DLL_DIRECTORY_COOKIE cookie = 0;
  bool restore_old_order = false;
  std::wstring current_directory;
  std::wstring plugin_path, plugin_value;
  const wchar_t *res = wcsrchr(lp.c_str(), L'');
  if (res)
  {
    plugin_path.assign(lp.c_str(), res);
    plugin_value.assign(++res);
    if (!plugin_path.empty())
    {
      if (add_dll_directory && remove_dll_directory)
        cookie = (*add_dll_directory)(plugin_path.c_str());
      else if (set_dll_directory)
        restore_old_order = (*set_dll_directory)(plugin_path.c_str());
      else
      {
        current_directory.resize(MAX_PATH);
        GetCurrentDirectoryW(MAX_PATH, &current_directory[0]);
        if (!SetCurrentDirectoryW(plugin_path.c_str()))
          current_directory.clear();
      }
    }
  }
  else
    plugin_value = lp;
  HMODULE module = (*load_library_api)(plugin_value.c_str());
  if (!module && error) {
    // GetLastError() needs to be called immediately after |load_library_api|.
    error->code = GetLastError();
  }
  if (remove_dll_directory)
  {
    if (cookie)
      (*remove_dll_directory)(cookie);
  }
  else if (set_dll_directory)
  {
    if (restore_old_order)
      (*set_dll_directory)(NULL);
  }
  else if (!current_directory.empty())
    SetCurrentDirectoryW(current_directory.c_str());
  return module;
}