Reference Manual
don't qi qi addref t*, dont_queryinterface(t*) do_queryinterface(nsisupports*), do_queryinterface(nsisupports*, nsresult*) do_queryreferent(nsiweakreference*), do_queryreferent(nsiweakreference*, nsresult*) don't addref dont_addref(t*), getter_addrefs(t*) n/a e.g., one of the possibilities for assigning into an nscomptr, but you don't want to addref the pointer you are assigning (because it has already been addrefed for some reason) is dont_addref(t*) found at the intersection of "don't addref" and "don't qi".
...nsresult rv; nscomptr<nsifoo> foo( do_queryinterface(abarptr, &rv) ); // or foo = do_queryinterface(abarptr, &rv); nscomptr<t> = dont_addref( t* ), nscomptr<t> = getter_addrefs( t* ) sometimes, you happen to have a pointer lying around that's already addrefed, but you want to put it into an nscomptr.
... nscomptr<nsifoo> foo( getter_addrefs(createafoo()) ); // |getter_addrefs| is a synonym for |dont_addref| that may look better to // you when applied to functions that return |addref|ed pointers nscomptr<nsifoo> foo( dont_addref(createafoo()) ); // or, maybe you don't like it better...
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Starting WebLock
nscomptr<nsicategorymanager> catman; rv = servman->getservicebycontractid(ns_categorymanager_contractid, ns_get_iid(nsicategorymanager), getter_addrefs(catman)); if (ns_failed(rv)) return rv; there are two service getters on the nsiservicemanager interface: one that takes a cid and another interface that takes a contract id.
... const nsmodulecomponentinfo *info) { nsresult rv; nscomptr<nsiservicemanager> servman = do_queryinterface((nsisupports*)acompmgr, &rv); if (ns_failed(rv)) return rv; nscomptr<nsicategorymanager> catman; rv = servman->getservicebycontractid(ns_categorymanager_contractid, ns_get_iid(nsicategorymanager), getter_addrefs(catman)); if (ns_failed(rv)) return rv; char* previous = nsnull; rv = catman->addcategoryentry("xpcom-startup", "weblock", weblock_contractid, pr_true, pr_true, &previous); if (previous) nsmemory::free(previous); retur...
... const nsmodulecomponentinfo *info) { nsresult rv; nscomptr<nsiservicemanager> servman = do_queryinterface((nsisupports*)acompmgr, &rv); if (ns_failed(rv)) return rv; nscomptr<nsicategorymanager> catman; rv = servman->getservicebycontractid(ns_categorymanager_contractid, ns_get_iid(nsicategorymanager), getter_addrefs(catman)); if (ns_failed(rv)) return rv; rv = catman->deletecategoryentry("xpcom-startup", "weblock", pr_true); return rv; } ns_generic_factory_constructor(weblock) static const nsmodulecomponentinfo components[] = { { "weblock", weblock_cid, weblock_contractid, weblockconstructor, weblockregi...
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Getting Started Guide
you have to `annotate' the nscomptr with the getter_addrefs directive.
...differences: apply getter_addrefs when using an nscomptr as a `out parameter'.
... nscomptr<nsifoo> foo; getfoo(getter_addrefs(foo)); that's it.
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Working with Multiple Versions of Interfaces
nscomptr<nsiaccessible> accnode; rv = refp->getaccessiblefor(node, getter_addrefs(accnode)); if(ns_failed(rv)){ return self; } void *wh = null; nscomptr<nsiaccessibledocument> accdocnode; accdocnode = do_queryinterface(accnode, &rv); if(ns_failed(rv)){ return self; } rv = accdocnode->getwindowhandle(&wh); if(ns_succeeded(rv)){ self = static_cast<hwnd>(wh); } return self; } this approach worked, as is, for versions as early as firefox 1.5.
... hwnd gethwndb(nsidomnode *node){ hwnd self = null; nsresult rv; nscomptr<nsicomponentmanager> compmgr; rv = ns_getcomponentmanager(getter_addrefs(compmgr)); if (ns_failed(rv)){ return self; } nscomptr<nsiaccessibleretrieval> refp; rv = compmgr->createinstancebycontractid(accretcid, 0, iar_iid_old, getter_addrefs(refp)); if (ns_failed(rv)){ return self; } nscomptr<nsiaccessible> accnode; rv = refp->getaccessiblefor(node, getter_addrefs(accnode)); if(ns_failed(rv)){ return self; } void *wh = null; nscomptr<nsiaccessibledoc...
...ument> accdocnode; rv = accnode->queryinterface(iad_iid_old, getter_addrefs(accdocnode)); if(ns_failed(rv)){ return self; } rv = accdocnode->getwindowhandle(&wh); if(ns_succeeded(rv)){ self = static_cast<hwnd>(wh); } return self; } there is good news and bad news.
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XPCOM array guide
void notifyobservers(nsiarray* aarray) { pruint32 length; aarray->getlength(&length); for (pruint32 i=0; i<length; ++i) { nscomptr<nsimyobserver> element; aarray->queryelementat(i, ns_get_iid(nsielement), getter_addrefs(element)); element->observe(); } } a simpler option is to use the helper do_queryelementat which is typesafe.
...// get the array nscomptr<nsiarray> array; foo->getelements(getter_addrefs(array)); // make an enumerator nscomptr<nsisimpleenumerator> enumerator; array->enumerate(getter_addrefs(enumerator)); // now enumerate the elements ...
...nscomptr<nsistringenumerator> enumerator; ns_newstringenumerator(getter_addrefs(enumerator), melementnames); // now call a method on "this" that has a known behavior processnames(enumerator); // now enumerator is used up, and can be released ...
... ns_imethod getstrings(nsistringenumerator** aresult); private: nscstringarray melementnames; }; ns_imethodimp nsfoo::getstrings(nsistringenumerator** aresult) { nscomptr<nsiutf8stringenumerator> enumerator; nsresult rv = ns_newutf8stringenumerator(getter_addrefs(enumerator), melementnames, this); ns_ensure_success(rv, rv); return callqueryinterface(enumerator, aresult); } obsolete arrays and enumerators nsisupportsarray nsienumerator (includes nsibidirectionalenumerator) ...

Finishing the Component
const nsmodulecomponentinfo *info) { nsresult rv; nscomptr<nsiservicemanager> servman = do_queryinterface((nsisupports*)acompmgr, &rv); if (ns_failed(rv)) return rv; nscomptr<nsicategorymanager> catman; servman->getservicebycontractid(ns_categorymanager_contractid, ns_get_iid(nsicategorymanager), getter_addrefs(catman)); if (ns_failed(rv)) return rv; char* previous = nsnull; rv = catman->addcategoryentry("xpcom-startup", "weblock", weblock_contractid, pr_true, pr_true, &previous); if (previous) nsmemory::free(previous); rv = c...
...the code for getting the io service from the service manager looks like this: // get a pointer to the ioservice rv = servman->getservicebycontractid("@mozilla.org/network/io-service;1", ns_get_iid(nsiioservice), getter_addrefs(mioservice)); once you have this interface pointer, you can easily create nsiuri objects from a string, as in the following snippet: nscomptr<nsiuri> uri; nsembedcstring urlstring(node->urlstring); mioservice->newuri(urlstring, nsnull, nsnull, getter_addrefs(uri)); this code wraps a c-string with a nsembedcstring, which you'll recall i...
... *_retval = pr_false; nsresult rv; nscomptr<nsiservicemanager> servman; rv = ns_getservicemanager(getter_addrefs(servman)); if (ns_failed(rv)) return rv; nscomptr<nsiioservice> mioservice; // get a pointer to the ioservice rv = servman->getservicebycontractid("@mozilla.org/network/io-service;1", ns_get_iid(nsiioservice), getter_addrefs(mioservice)); if (ns_failed(rv)) return rv; urlnode* node = mrooturlnode; ...
... prbool match = pr_false; while (node) { nscomptr<nsiuri> uri; nsembedcstring urlstring(node->urlstring); rv = mioservice->newuri(urlstring, nsnull, nsnull, getter_addrefs(uri)); // if anything bad happens, just abort if (ns_failed(rv)) return rv; nsembedcstring host; uri->gethost(host); if (strcmp(hosttoload.get(), host.get()) == 0) { // match found.

Storage
rvices.jsm"); components.utils.import("resource://gre/modules/fileutils.jsm"); let file = fileutils.getfile("profd", ["my_db_file_name.sqlite"]); let dbconn = services.storage.opendatabase(file); // will also create the file if it does not exist likewise, the c++ would look like this: nscomptr<nsifile> dbfile; rv = ns_getspecialdirectory(ns_app_user_profile_50_dir, getter_addrefs(dbfile)); ns_ensure_success(rv, rv); rv = dbfile->append(ns_literal_string("my_db_file_name.sqlite")); ns_ensure_success(rv, rv); nscomptr<mozistorageservice> dbservice = do_getservice(moz_storage_service_contractid, &rv); ns_ensure_success(rv, rv); nscomptr<mozistorageconnection> dbconn; rv = dbservice->opendatabase(dbfile, getter_addrefs(dbconn)); ns_ensure_success(rv, rv); note: moz_stora...
...similarly, the c++ looks like this: nscomptr<mozistoragestatement> statement; rv = dbconn->createstatement(ns_literal_cstring("select * from table_name where column_name = ?1"), getter_addrefs(statement)); ns_ensure_success(rv, rv); this example uses the numbered placeholder indexed by zero for a parameter to be bound later (described in binding parameters).
... c++ example: nscomptr<mozistoragestatement> statement; rv = mdbconn->createstatement(ns_literal_cstring("select * from table_name where id = ?1"), getter_addrefs(statement)); ns_ensure_success(rv, rv); rv = statement->bindint32parameter(0, 1234); ns_ensure_success(rv, rv); note: numerical indexes for parameters are always one less than the number you write in the sql.
... nsresult rv = mdbconn->createstatement(ns_literal_cstring("delete from table_name"), getter_addrefs(statement)); ns_ensure_success(rv, rv); return statement->execute(); // once this function returns, mspecialstatement will be reset, and statement will // be destroyed.

Creating Custom Events That Can Pass Data
wwatcher->getactivewindow(getter_addrefs(awindow)); //get the active window.
... awindow->getdocument(getter_addrefs(adoc)); //get the document from the window.
... docevent->createevent(ns_literal_string("nsdommyevent"), getter_addrefs(event)); //create the event event->initevent(ns_literal_string("nsdommyevent"), pr_true, pr_true); //initialize it twindow = do_queryinterface(awindow); //use the window for a target.

Mozilla DOM Hacking Guide
nscomptr<nsidomwindow> window(do_queryinterface(native)); ns_ensure_true(window, ns_error_unexpected); nscomptr<nsidomlocation> location; rv = window->getlocation(getter_addrefs(location)); ns_ensure_success(rv, rv); // use the dom to get the location object of the window object.
... nscomptr<nsisupports> native; wrapper->getnative(getter_addrefs(native)); // get the pointer to the content object that was wrapped.
... nscomptr<nsidomlocation> location; nsresult rv = window->getlocation(getter_addrefs(location)); ns_ensure_success(rv, rv); // get the location object for this window.

Using XPCOM Utilities to Make Things Easier
using smart pointers, the code above can be simplified to: { nscomptr<nsisupports> value; object->method(getter_addrefs(value)); if (!value) return; // ...
...when you pass them to a getter, you must do something special, however: you must wrap the variable with the function getter_addrefs, as in the example above.
...this is a common pattern when you have a local nscomptr in a function and you must pass back a reference to it, as in the following: someclass::get(nsisupports** aresult) { if (!aresult) return ns_error_null_pointer; nscomptr<nsisupports> value; object->method(getter_addrefs(value)); *aresult = value.get(); ns_if_addref(*aresult); return ns_ok; } the first thing that this method does is check to see that the caller passed a valid address.

Introduction to XPCOM for the DOM
nscomptr<nsifoo> ifooptr; getinterfaceifoo(getter_addrefs(ifooptr)); ifooptr->functionofnsifoo(); the peculiar syntax, getter_addrefs(pointer), is the nscomptr counterpart to the usual "&" (address-of) c operator.
...we have already seen what getter_addrefs() does to nscomptr's.
...i had to use the second solution: nscomptr<nsicontent> content = getter_addrefs(ns_static_cast(nsicontent*, this)); // or, if you want to do the refcounting yourself, nsicontent *content = ns_static_cast(nsicontent*, this); the second form should be used with care, and is recommended only for advanced xpcom'ers.

Using Dependent Libraries In Extension Components - Archive of obsolete content
// assume that we're in <extensiondir>/components, and we want to find // <extensiondir>/libraries nscomptr<nsifile> libraries; rv = alocation->getparent(getter_addrefs(libraries)); if (ns_failed(rv)) return rv; nscomptr<nsilocalfile> library(do_queryinterface(libraries)); if (!library) return ns_error_unexpected; library->setnativeleafname(ns_literal_cstring("libraries")); library->appendnative(ns_literal_cstring("dummy")); // loop through and load dependent libraries for (char const *const *dependent = kdependentlibraries; *depe...
... // assume that we're in <extensiondir>/components, and we want to find // <extensiondir>/libraries nscomptr<nsifile> libraries; rv = alocation->getparent(getter_addrefs(libraries)); if (ns_failed(rv)) return rv; nscomptr<nsilocalfile> library(do_queryinterface(libraries)); if (!library) return ns_error_unexpected; library->setnativeleafname(ns_literal_cstring("libraries")); library->appendnative(ns_literal_cstring("dummy")); nscstring path; // loop through and load dependent libraries for (char const *const *dependent = kdependentlibraries; ...

Editor Embedding Guide - Archive of obsolete content
nscomptr<nsieditingsession> editingsession; nsiwebbrowser->do_getinterface(getter_addrefs(editingsession)); if (editingsession) editingsession->makewindoweditable(domwindow, "html", pr_true); the valid editor types are: "text" (similar to notepad or a textarea; does not allow for html) "textmail" (similar to "text" but html can be inserted; intended for plaintext mail usage and handling of citations) "html" (this is the default type if no type is specified; it allows for all htm...
...get the nsicommandmanager from the nsiwebbrowser using do_getinterface: nscomptr<nsicommandmanager> commandmanager; nsiwebbrowser->do_getinterface(getter_addrefs(commandmgr)); 2.

Multiprocess on Windows
there is also a mozilla::mscom::getter_addrefs() function that allows these pointers to receive outparams.
... simple example now you know about mainthreadhandoff::wrapinterface and about the smart pointers, you're ready to wrap an interface: accessible* myaccessible = ....; mozilla::mscom::stauniqueptr<iaccessible> acctowrap; myaccessible->getnativeinterface(mozilla::mscom::getter_addrefs(acctowrap)); mozilla::mscom::proxyuniqueptr<iaccessible> wrapped; hresult hr = mozilla::mscom::mainthreadhandoff::wrapinterface(mozilla::move(acctowrap), mozilla::mscom::getter_addrefs(wrapped)); if (failed(hr)) { // handle your error here } // the wrapped interface should be given to the at from within the mta.

nsICategoryManager
nsresult printallcategories() { nsresult rv; nscomptr<nsiservicemanager> svcmgr; rv = ns_getservicemanager(getter_addrefs(svcmgr)); if (ns_failed(rv)) return rv; nscomptr<nsicategorymanager> catmgr; rv = svcmgr->getservicebycontractid(ns_categorymanager_contractid, ns_get_iid(nsicategorymanager), getter_addrefs(catmgr)); if (ns_failed(rv)) return rv; nscomptr<nsisimpleenumerator> cats; rv = catmgr->enumeratecatego...
...ries(getter_addrefs(cats)); if (ns_failed(rv)) return rv; prbool hasmore; while (ns_succeeded(cats->hasmoreelements(&hasmore) && hasmore) { nscomptr<nsisupports> elem; cats->getnext(getter_addrefs(elem)); nscomptr<nsisupportscstring> category = do_queryinterface(elem, &rv); if (ns_failed(rv)) break; nsembedcstring categoryname; rv = category->getdata(categoryname); if (ns_failed(rv)) break; printf("%s\n", categoryname.get()); } return ns_ok; } this snippet shows how to print out a list of all categories in javascript.