c++ - 如何序列化 VARIANT 或 BSTR？

Question

我正在尝试找出一些 COM 编码功能。最终，我想将一个深度嵌套的变体数组保存到文件中，但我首先尝试使用一个简单的字符串。我意识到这些 API 用于远程过程调用，但我希望这种序列化也适用于文件持久化。

我经常使用 Excel VBA，发现这个序列化 API 真是大开眼界。

下面的代码将一个 BSTR 序列化到一个缓冲区，缓冲区被复制，它将作为保存到文件和从文件加载的替代品。

当前的问题是 BSTR_UserUnmarshal 在 RPCMarshalling.exe 中的 0x7631C762 (KernelBase.dll) 处引发异常 未处理的异常:0x00000057:参数不正确。发生了

我的语法可能有误，因为我正在使用示例代码片段。目标是使用 RPC 序列化 API 调用从 srctest 获取字符串到 desttest。

// RPCMarshalling.cpp : This file contains the 'main' function. Program execution begins and ends there.
//

#include "pch.h"
#include <iostream>

//https://searchcode.com/file/140723732/dlls/oleaut32/tmarshal.c#l-818

typedef struct _marshal_state {
    LPBYTE  base;
    int     size;
    int     curoff;
} marshal_state;


int main()
{
    ::CoInitialize(0);

    CComBSTR srctest("Hello");
    marshal_state srcbuf;
    memset(&srcbuf, 0, sizeof(srcbuf));
    ULONG flags = MAKELONG(MSHCTX_DIFFERENTMACHINE, NDR_LOCAL_DATA_REPRESENTATION);

    ULONG size = ::BSTR_UserSize(&flags, 0, &srctest);

    DWORD newsize = max(size, 256);
    (&srcbuf)->base = (LPBYTE)HeapAlloc(GetProcessHeap(), HEAP_ZERO_MEMORY, newsize);
    if (!(&srcbuf)->base)
        return E_OUTOFMEMORY;

    ::BSTR_UserMarshal(&flags, (&srcbuf)->base + (&srcbuf)->curoff, &srctest);
    (&srcbuf)->curoff = size;


    std::cout << "Hello World!\n" << size << "\n";


    marshal_state destbuf;
    memset(&destbuf, 0, sizeof(destbuf));

    (&destbuf)->base = (LPBYTE)HeapAlloc(GetProcessHeap(), HEAP_ZERO_MEMORY, newsize);
    if (!(&destbuf)->base)
        return E_OUTOFMEMORY;

    /* pretend we are loading from file saved by src buffer */
    RtlCopyMemory((&destbuf)->base, (&srcbuf)->base, newsize);


    CComBSTR desttest("");
    BSTR deststring;

    try
    {
        unsigned char *buffer;
        buffer = ::BSTR_UserUnmarshal(&flags, (&destbuf)->base, &deststring);
    }
    catch (int e)
    {
        std::cout << "Error:" << e << "\n" << size << "\n";
    }



    ::CoUninitialize();

}

Answer 1

实现序列化 Variant 目标的替代方法(根据 OP 的问题文本)正在进行中，使用 Simon Mourier 关于 StgSerializePropVariant 的建议

int main()
{
    ::CoInitialize(0);

    CComVariant srctest("Hello");

    SERIALIZEDPROPERTYVALUE* serialized;
    ULONG cb;
    ::StgSerializePropVariant((PROPVARIANT*)&srctest, &serialized, &cb);

    CComVariant pvDest;
    ::StgDeserializePropVariant(serialized, cb, (PROPVARIANT*)&pvDest);

    CoTaskMemFree(serialized);

    CComBSTR strDest(pvDest.bstrVal);
    std::cout << "This got serialized:\n" << LPCSTR(_bstr_t(strDest, true)) << "\n";

    ::CoUninitialize();
}