C ++在编译时创建BSTR /在编译时将长度插入字符串？ [英] C++ Create BSTR at compile time / insert length into string at compile time?

问题描述

是否可以使用宏魔法或TMP在编译时将长度插入到字符串中？

Is it possible using macro magic or TMP to insert the length into a string at compile time?

例如：

const wchar_t* myString = L"Hello";

我希望缓冲区实际包含[length] [string constant]。

I would want the buffer to actually contain "[length] [string constant]".

我使用MSVC 2010缺少constexpr。我想，必须有一些技巧，使这项工作，它可能做：

I'm using MSVC 2010 which lacks constexpr. I figured there must be some trick to make this work as its possible to do:

const wchar_t* myString = L"\x005Hello";

我的尝试到目前为止：

template<int Size>
wchar_t* toBstr(const wchar_t* str)
{
    #pragma pack(push)
    #pragma pack(1)
    struct BStr
    {
       int len;
       wchar_t data[Size];
    };
    #pragma pack(pop)

  static BStr ret;
  ret.len = Size;

  // don't want to have to copy here, how else could this work??
  //ret.data = str;

  return ret.data;
 }

 const wchar_t* m = toBstr<_countof(L"Hello")>(L"Hello");

这个问题似乎相关：

a href =http://stackoverflow.com/questions/4693819/c-template-string-concatenation> C ++范本字串连结

C++ template string concatenation

但不是concat for两个字符串常量，而是从第二个长度生成的常数：）

But not concat for two string constants, rather a constant generated from the length of the 2nd :)

推荐答案

我使用这个简单的宏：

#define DECLARE_BSTR(Variable, String)\
struct                                \
{                                     \
    uint32_t uLength;                 \
    OLECHAR szData[sizeof(String)];   \
}                                     \
Variable = {sizeof(String) - sizeof(OLECHAR), String};

示例：

ITaskFolder *pTaskFolder;
DECLARE_BSTR(static bstrTaskFolderName, L"\\");
if (SUCCEEDED(pTaskService->GetFolder(bstrTaskFolderName.szData, &pTaskFolder)))

---

可以用来代替 BSTR 的变体，即没有 .szData ：

---

Variant which can be used in place of a BSTR, i.e. without .szData:

#define DECLARE_BSTR(Variable, String)               \
struct                                               \
{                                                    \
    uint32_t uLength;                                \
    OLECHAR szData[sizeof(String)];                  \
    operator const OLECHAR *() const {return szData;}\
    operator       OLECHAR *()       {return szData;}\
}                                                    \
Variable = {sizeof(String) - sizeof(OLECHAR), String};

示例：

ITaskFolder *pTaskFolder;
DECLARE_BSTR(static bstrTaskFolderName, L"\\");
if (SUCCEEDED(pTaskService->GetFolder(bstrTaskFolderName, &pTaskFolder)))

这篇关于C ++在编译时创建BSTR /在编译时将长度插入字符串？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！