Enumerating all the programs that can launch a particular protocol

Raymond Chen

Today’s Little Program is a variation on the one from last time. This time, instead of enumerating all the handlers for a file extension, we enumerate all the handlers for a protocol. We then open a Web site with that chosen program.

Start with the program from last time and make these changes:

std::vector<CComPtr<IAssocHandler>> LoadHandlers(
  PCWSTR extension)
  // ASSOC_FILTER filter
  std::vector<CComPtr<IAssocHandler>> handlers;
  CComPtr<IEnumAssocHandlers> enumerator;
    L"http", IID_PPV_ARGS(&enumerator));
  for (CComPtr<IAssocHandler> handler;
       enumerator->Next(1, &handler, nullptr) == S_OK;
       handler.Release()) {
  return handlers;

The SHAssoc­Enum­Handlers­ForProtocol­By­Application function does not have a filter option, so we delete that parameter from Load­Handlers.

The Choose­Handler function is unchanged.

int __cdecl main(int, char**)
  CCoInitialize init;
  ProcessReference ref;

  auto handlers = LoadHandlers(L"http");
  auto selection = ChooseHandler(handlers, false);

  if (selection < handlers.size()) {
    CComPtr<IDataObject> dobj;
    GetUIObjectOfFile(nullptr, L"http://www.microsoft.com/",
  return 0;

This version is shorter because there is no filter option, so we just load up all the handlers, pick one, and invoke it.

Notice that we are using Get­UI­Object­Of­File for something that isn’t a file. If you go back to that function, you’ll see that there’s nothing in it that actually requires a file. It can accept any parseable name. A more accurate name for the function would have been Get­UI­Object­Of­Parsing­Name, but it’s too late now.


Discussion is closed.

Feedback usabilla icon