I have an ADO Stream, opened in binary mode, and I want to write binary data to that stream. Below is a test program that compiles as a console application in VC++ 2008. It simply creates a new stream, opens it in binary mode, and attempts to write some data. Write() fails with error 0x800A0BB9 (invalid argument). I have no idea why.

If I open the stream in text mode and use WriteText, it works with no problem. If I open the stream in binary mode and use WriteText, it fails as expected (illegal operation). But, no matter what mode I open the stream in, when I use Write, it fails.

I have tried other VARIANT types besides the one in the code snippet below (arrays, other simple types), all with the same results. (In my actual program, I'm attempting to write an array of bytes as a SAFEARRAY wrapped in a VARIANT).

I've also tried setting the stream mode before opening it, with no effect. I have verified that the stream is open in binary mode by getting it's type and checking that it is adTypeBinary.

What am I doing wrong here? Why is Write failing every time? How do I write binary data to an ADO Stream?

In case you are wondering, the reason I am doing this is because I'm using CDOSYS to send emails with attachments, and I'm constructing attachments from blocks of arbitrary binary data in memory. The Stream in question is the decoded content stream from an IBodyPart. However, it seems to have nothing to do with CDOSYS, as I'm having the same problem in the test case below.

Thanks!

(Edit: Question rewritten -- it's pretty much the same as my first comment below now)

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#import "C:\Program Files\Common Files\System\ado\msado15.dll" no_namespace raw_interfaces_only
#include <cstdio>
#include <stdexcept>
#include <string>
 
using namespace std;
 
 
struct auto_coinit {
    auto_coinit () { CoInitializeEx(NULL, COINIT_MULTITHREADED); }
    ~auto_coinit () { CoUninitialize(); }
};
 
 
struct error_code : public runtime_error {
    static string estr (const char *w, DWORD c) { 
        char s[100]; 
        _snprintf_s(s, _TRUNCATE, "%s: 0x%08lX", w, c); 
        return s; 
    }
    error_code (const char *w, DWORD c) : runtime_error(estr(w, c)) { }
};
 
 
int main () {
 
    try {
 
        auto_coinit coinit;
        _StreamPtr s;
        HRESULT r;
 
        r = s.CreateInstance(__uuidof(Stream));
        if (FAILED(r))
            throw error_code("CreateInstance", r);
 
        // stream test code starts here (open, set binary, write)
 
        r = s->Open(vtMissing, adModeUnknown, adOpenStreamUnspecified, _bstr_t(), _bstr_t());
        if (FAILED(r))
            throw error_code("Open", r);
 
        r = s->put_Type(adTypeBinary);
        if (FAILED(r))
            throw error_code("put_Type", r);
 
        _variant_t v;
        v.vt = VT_UI1;
        v.bVal = 'x';
 
        r = s->Write(v);
        if (FAILED(r))
            throw error_code("Write", r);
 
        // stream test code ends here
 
    } catch (const exception &x) {
 
        fprintf(stderr, "error: %s\n", x.what());
 
    }
 
    printf("finished\n");
    getchar();
 
}