POSTing an XML string

[motocross1]

I need to POST a normal-everyday XML data string to a website.

I FAIL when I POST with WinInet using:

string Headers="Content-Type: application/xml";
string POSTdata="<?xml version=\"1.0\" encoding=\"utf-8\"?><note><to>Webserver</to><from>Me</from><re>My XML data</re></note>";
HttpSendRequest(hReq, Headers.c_str(), (DWORD)-1, (LPVOID)POSTdata.c_str(), strlen(POSTdata.c_str()))

I SUCCEED when I POST with IXMLHTTPRequest using:

http->setRequestHeader("Content-Type", "application/xml");
http->send(POSTdata.c_str());

I read that IXMLHTTPRequest encodes the XML to UTF-8:
send Method (IXMLHTTPRequest)

If the input type is an XML DOM object, the response is encoded according to the encoding attribute on the <? declaration in the document. If there is no XML declaration or encoding attribute, UTF-8 is assumed.

But, I am not sure if WinInet can even encode to UTF-8:
Issue in sending HTTP Request with UTF-8 URI using WinINet

It would be very helpful if I can get any documentation stating that Windows APIs don't support UTF-8.

For me though, here is why I am confused:
UTF-8 - Wikipedia, the free encyclopedia

The first 128 characters of Unicode, which correspond one-to-one with ASCII, are encoded using a single octet with the same binary value as ASCII, making valid ASCII text valid UTF-8-encoded Unicode as well.

So, what is the difference?
Byte versus Byte, character versus character.
Shouldn't my XML string be the same in UTF-8 versus the original C++ string?

If the answer is: "Yes, they should be the same" - then, why does WinInet FAIL?
If the answer is: "No, they are actually different" - then, what does my XML look like in UTF-8?

Thanks

[motocross1]

Note:
WinInet doesn't FAIL in making the POST.
It's just that the website rejects the POST as being incorrect data.

[Salem]

Wireshark · Go deep.
Then you can see what the resulting messages are "on the wire", and compare the "good" with the "bad".

[motocross1]

Unfortunately, the website that I am POSTing to is HTTPS.

But that does give me an idea...
Maybe I can POST to a friend's website and see the data that way.

Thank-you for spurring my mind.