c ++用于VB6库的BSTR转换 [英] c++ BSTR conversion for VB6 library

问题描述

这是我遇到的问题的一个例子。



C ++ Lib

Here is an example of a problem I am having.

C++ Lib

BSTR testlib::f4str(const long fPtr)
{
_variant_t retVal = dataRS->Fields->Item[_variant_t(fPtr)]->Value;
BSTR retStr = SysAllocStringLen(retVal.bstrVal,dataRS->Fields->Item[_variant_t(fPtr)]->DefinedSize);
    return retStr;
}

VB6函数

VB6 Function

Declare Function f4str$ Lib "testlib.dll" (ByVal fPtr&)

所以当我运行这个函数时，我会收回字符串，但每个字符都是字符串由SOH字符（标题的开头）分隔我将其视为无法呈现的小方框字符。我知道它是一个SOH，因为我把它放到一个为我呈现空白的编辑器中。



到目前为止我得到的结果是C ++中的BSTR是< b> 与VB6的BSTR不一样所以当我把它寄回去时我得到了。



应该注意的是，如果我只输入一个字符串输入并发回它工作正常..所以它只发生在我从_variant_t转换为BSTR。



提前感谢

So when i run this function i get back the string but every character of the string is seperated by a SOH character (start of header) i see it as a small box charcter that cannot be rendered. I know its an SOH because I put it into an editor that renders whitespace for me.

What I have sorta worked out so far is that the BSTR in C++ is not the same as the BSTR for VB6 so when I send it back I get that.

It should be noted that If I just type a string in and send it back it works fine.. so it only happens when I convert from _variant_t to BSTR.

thanks in advance

推荐答案

Libtestlib.dll（ByVal fPtr&）

Lib "testlib.dll" (ByVal fPtr&)

所以当我运行这个功能的时候我获取字符串，但字符串的每个字符都由SOH字符（标题的开头）分隔，我将其视为无法呈现的小方框字符。我知道它是一个SOH，因为我把它放到一个为我呈现空白的编辑器中。



到目前为止我得到的结果是C ++中的BSTR是< b> 与VB6的BSTR不一样所以当我把它寄回去时我得到了。



应该注意的是，如果我只输入一个字符串输入并发回它工作正常..所以它只发生在我从_variant_t转换为BSTR。



提前感谢

So when i run this function i get back the string but every character of the string is seperated by a SOH character (start of header) i see it as a small box charcter that cannot be rendered. I know its an SOH because I put it into an editor that renders whitespace for me.

What I have sorta worked out so far is that the BSTR in C++ is not the same as the BSTR for VB6 so when I send it back I get that.

It should be noted that If I just type a string in and send it back it works fine.. so it only happens when I convert from _variant_t to BSTR.

thanks in advance

将您的字符串接口更改为BSTR或char *类型，并始终避免将非平凡对象作为字符串（不是char的数组）进行交换。



VB 6是一个痛苦，但如果你坚持使用大代码库，我想知道为什么没有一些工作函数。



永远不要使用它们之间的对象C ++和VB6。这个功能只适用于VB.net：mad：



几乎是什么dataRS？

change your string interface to BSTR or char* type and always avoid to interchange non-trivial objects as strings (which arent arrays of char).

VB 6 is a pain, but if you are to stuck on it with the big code base, I wonder why there isnt some working functions for that.

Never ever use objects betweens C++ and VB6. This features only works with VB.net :mad:

What the heck is dataRS?

从一个字符串返回一个字符串dll到VB6。



在VB6中声明

To return a String from a dll to VB6.

Declare in VB6

Public Declare Function QueryString Lib "lihelper" Alias "_QueryString@4" (ByVal key As String) As String

在VB6中调用

Call in VB6

Dim s as String : s = QueryString("find me")

在C ++ DLL中定义

Define in C++ DLL

extern "C" __declspec(dllexport) BSTR __stdcall QueryString(LPCSTR key{
  const std::string response(key? odbc::sql::query(key) : std::string(""));
  return SysAllocStringByteLen(response.c_str(), response.size());
}

Vb6将始终从DLL转换返回的字符串，就好像它是多字节的，这就是为什么你的Unicode字符串只包含它们的第一个字符（除非它是> 0xFF当然）。

通常我会分配一个合理预定义大小的缓冲区，并查看返回的数据是否合适。返回所需大小的功能。如果需求更大，我会放弃并重新分配......

Vb6 will always convert a returning string from a DLL as if it's multibyte, that's why your Unicode-strings will only contain their first character (unless it's >0xFF of course).
Normally I allocates a buffer of reasonable predefined size and sees if the returning data fits. The function the returning the needed size. If the needs are greater, I'll give in and reallocates ...

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