{"id":92191,"date":"2015-11-30T07:00:00","date_gmt":"2015-11-30T22:00:00","guid":{"rendered":"https:\/\/blogs.msdn.microsoft.com\/oldnewthing\/20151130-00\/?p=92191\/"},"modified":"2019-03-13T12:22:22","modified_gmt":"2019-03-13T19:22:22","slug":"20151130-00","status":"publish","type":"post","link":"https:\/\/devblogs.microsoft.com\/oldnewthing\/20151130-00\/?p=92191","title":{"rendered":"Enumerating all the programs that can open a particular file extension"},"content":{"rendered":"

Today’s Little Program enumerates all the applications which are registered for a particular file extension and lets the user choose one. We then open a file with that chosen program. <\/p>\n

As always, Little Programs do little to no error checking. <\/p>\n

\n#include <windows.h>\n#include <ole2.h>\n#include <shlobj.h>\n#include <atlbase.h>\n#include <atlalloc.h>\n#include <vector>\n#include <iostream>\n\nstd::vector<CComPtr<IAssocHandler>> LoadHandlers(\n  PCWSTR extension,\n  ASSOC_FILTER filter)\n{\n  std::vector<CComPtr<IAssocHandler>> handlers;\n  CComPtr<IEnumAssocHandlers> enumerator;\n  SHAssocEnumHandlers(extension, filter, &enumerator);\n  for (CComPtr<IAssocHandler> handler;\n       enumerator->Next(1, &handler, nullptr) == S_OK;\n       handler.Release()) {\n       handlers.push_back(handler);\n  }\n  return handlers;\n}\n<\/pre>\n
The Load­Handlers<\/code> function shows off the meat of the program: We use SHAssoc­Enum­Handlers<\/code> to enumerate all the handlers for a particular extension. The results get saved into a vector. <\/p>\n
\nauto\nChooseHandler(\n  const std::vector<CComPtr<IAssocHandler>>& handlers,\n  bool allowChooseMore) -> decltype(handlers.size())\n{\n  decltype(handlers.size()) i;\n  for (i = 0; i < handlers.size(); i++) {\n    CComHeapPtr<wchar_t> name;\n    handlers[i]->GetUIName(&name);\n    std::wcout << i << L\": \" << static_cast<PCWSTR>(name)\n                             << std::endl;\n  }\n  if (allowChooseMore) {\n    std::wcout << i << L\": Show more handlers\" << std::endl;\n    i++;\n  }\n\n  decltype(handlers.size()) selection;\n  std::wcin >> selection;\n  if (std::wcin.fail()) selection = i + 1;\n  return selection;\n}\n<\/pre>\n
The Choose­Handler<\/code> function prints the vector of handlers (and optionally adds a “Show more handlers” option). It collects the user’s reply and returns it, using handlers.size()<\/code> to represent the “Show more handlers” option, if available. If the user’s input is invalid, we return a value that is out of range. (I’m assuming you don’t have four billion handlers.) <\/p>\n
\nint __cdecl main(int, char**)\n{\n  CCoInitialize<\/a> init;\n  ProcessReference<\/a> ref;\n\n  auto handlers = LoadHandlers(L\".txt\", ASSOC_FILTER_RECOMMENDED);\n  auto selection = ChooseHandler(handlers, true);\n  if (selection == handlers.size()) {\n    handlers = LoadHandlers(L\".txt\", ASSOC_FILTER_NONE);\n    selection = ChooseHandler(handlers, false);\n  }\n\n  if (selection < handlers.size()) {\n    CComPtr<IDataObject> dobj;\n    GetUIObjectOfFile<\/a>(nullptr, L\"C:\\\\windows\\\\win.ini\",\n                      IID_PPV_ARGS(&dobj));\n    handlers[selection]->Invoke(dobj);\n  }\n  return 0;\n}\n<\/pre>\n
And here’s the main function that ties everything together. <\/p>\n
After some initial throat-clearing, it loads up the recommended handlers for the .txt<\/code> file extension and lets the user choose from among them. <\/p>\n
If the user says “Show more handlers”, then we load up all handlers and try again. <\/p>\n
We then take the user’s selection and open WIN.INI<\/code> with that program. <\/p>\n
Exercise<\/b>: What is the purpose of the Process­Reference<\/code> object? <\/p>\n","protected":false},"excerpt":{"rendered":"
SHAssocEnumHandlers.<\/p>\n","protected":false},"author":1069,"featured_media":111744,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[1],"tags":[25],"class_list":["post-92191","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-oldnewthing","tag-code"],"acf":[],"blog_post_summary":"
SHAssocEnumHandlers.<\/p>\n","_links":{"self":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/92191","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/users\/1069"}],"replies":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/comments?post=92191"}],"version-history":[{"count":0,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/92191\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/media\/111744"}],"wp:attachment":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/media?parent=92191"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/categories?post=92191"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/tags?post=92191"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}