Can I use all the functionally I see exposed by the .TLH file?

Question

Background:

I have an existing code that uses functionality provided by Microsoft, to post XML data over HTTP. Specifically, IServerXMLHTTPRequest (included in MSXML3 and up) from msxml4.dll (COM). I am moving to msxml6.dll as msxml4.dll is not supported anymore (superseded by MSXML6). More information about MSXML versions.

Code:

#import "msxml6.dll"
using namespace MSXML2;
…
IServerXMLHTTPRequestPtr spIXMLHTTPRequest = NULL;
hr = spIXMLHTTPRequest.CreateInstance(__uuidof(ServerXMLHTTP40));

Problem:

When building my app with msxml4.dll as well as msxml6.dll the following is included in the msxml4.tlh and msxml6.tlh respectively:

struct __declspec(uuid("88d969c6-f192-11d4-a65f-0040963251e5"))
ServerXMLHTTP40;
    // [ default ] interface IServerXMLHTTPRequest2

As I understand, looking at msxml6.tlh, I can use ServerXMLHTTP40 (and not change the code to ServerXMLHTTP60) with msxml6.dll (same for DOMDocument40, FreeThreadedDOMDocument40, XMLSchemaCache40 etc.).

Now, searching the registry in a fresh Windows 7 Ultimate installation, I cannot find the uuid above. As a result, this code fails on this machine:

hr = spIXMLHTTPRequest.CreateInstance(__uuidof(ServerXMLHTTP40));

Questions:

If msxml6 is exposing ServerXMLHTTP40, why is it that I cannot find it in the registry? Can I use ServerXMLHTTP40 when msxml6 is installed (msxml4 is not installed)?

Need additional information? Just let me know. Thank you!

Answer 1

.TLH file (as a product of import from .TLB, which is in turn a compiled version of .IDL file) is a description of interfaces, structures, methods etc. which ones uses to talk through COM to another object. There is no guarantee or promise that the other party implementing these interfaces is installed or otherwise available, or even exists at all.

Yes you have the signatures defined for you convenience. You might need to install runtime that implements the functionality. MSXML 4 might need a separate install regardless of where you obtained the development details from.