Accessing the ihtmldocument interface of an html frame. Queryinterface is called in vb when it needs to verify that the object is indeed an ole automation object i. After some standard validation of the parameters that are passed in, an implementation of queryinterface checks the identifier of the requested interface against the list of supported interfaces. Tips for debugging com addrefrelease leaks its compiling. This way you can request an interface from a pointer to any unrelated com interface and check whether that request succeeded. Constructs a new ccomptr object with an iunknown pointer and an iid. So, generally object expose their public methods to developpers and container application by type library files. Internally constructor will call piunknown queryinterface to fetch interface pointer according to the iid. After that, this new ccomptr object can be used as an interface pointer itself.
Ccomptr is used to create a smart pointer based on an interface type ccomptr pitf praw. No matter you want to develop a simple database workflow application, or an large flowdiagram based system, our product will provide a complete solution for you. Some of the products that appear on this site are from companies from which quinstreet receives compensation. Hi, i am struggling with a problem for some time and i hope i can get some guidance here on the community forums. I know very little about com and nothing about atl but my guess is that you can just declare a ihtmldocument2 pdoc instead of the ccomptr spdoc because ccomptr is a pointer wrapper. As in the case of addref and release, the visual basic implementation of queryinterface is fairly straightforward, but you can never see it. Jan 16, 2020 tech support scams are an industrywide issue where scammers trick you into paying for unnecessary technical support services. The constructors that take an argument call addref on lp, if it isnt a null pointer.
Addref, release, queryinterface it implements gettypeinfocount, gettypeinfo, getidsofnames and invoke. Atl does provide a com smart pointer class named ccomqiptr, but it uses some atlspecific funtions inside so that it can not be used outside the atl environment. There are basically two sides to atlclientside support and objectside support. Because ccomptr and ccomqiptr do not hide calls to addref and release, this blind conversion causes a problem when the release is called through the dispatch smart pointer. How to get that idispatch interface you can read more here. If you have a ccomptr pco1, you dont call pco1isequalobjectpco2 because this invokes the operator defined in the ccomptr class which returns an automatically addref d version of the underlying com interface so that you can dereference it. Nov 19, 2019 ccomptr provides a specialization for idispatch that enables it to store pointers to com automation components and invoke the methods on the interface by using late binding. Queryinterface is wrapped so that you dont need the void casts and explicit iids. I need a class to run my version of queryinterface. Addref release are hidden, and the reference count is maintained behind the scenes so that the reference implied by the ccomptr instance is tied to the current program scope. The class is wizard generated, and inherits from idispatch. Ucancode software focuses on general application software development.
I find the getmotionstudymanager of iswmodeldocextension returns a idispatch object. The following example shows how to use ccomptr to instantiate a. For the method to be capable of interpreting its received parameters, the caller must specify the format of the data as well as its value. Feb 22, 2006 construct a new ccomptr object with an iunknown pointer and an iid, which represents the interface you are interested in. You call addref to ensure that it knows you are using the object so that it doesnt destroy it. Internally, a constructor will call piunknown queryinterface to fetch the interface pointer according to. That is, you dont need to worry about the life cycle of your com interface pointer.
However, it seems that sometimes smart pointers are too smart in particular, im referring to the secret queryinterfaceing assignment operator discussed by jared parsons on his blog. Tech support scams are an industrywide issue where scammers trick you into paying for unnecessary technical support services. Your question is better, but apparently nobody knows the answer or nobody wants to explain it. The smart pointer ccomqiptr here is simply a quick means of calling queryinterface to get idispatch regardless of how its implemented. A simple com server that is based on multiple inheritance. The interop runtime code will insert the appropriate method calls for reference counting when the managed proxy objects are created and freed, and will translate typecast, is, and as operators into calls to queryinterface. Calling addref increments the reference count and release decrements it. Addref and release just increment and decrement a use counter so that the com object knows when it still has users, and you can mostly ignore them. Find answers to iunknown to idispatch from the expert community at experts exchange. Ccomqiptr is for cases when you want to call queryinterface in a. You can help protect yourself from scammers by verifying that the contact is a microsoft agent or microsoft employee and that the phone number is an official microsoft global customer service number. Atl uses ccomqiptr and ccomptr to manage com interface pointers.
When you are done you release to tell it you are done with the object. Contribute to go olego ole development by creating an account on github. In computer programming, the iunknown interface is the fundamental interface in the. Ccomptrisequalobject wont compile autodesk community. By far the largest portion of support is on the object side because of all the code necessary to implement activex controls. Idispatch this interface provides namebased dynamic method dispatch for. Iunknown and retval rewriting today, were going to finish out the definition of iuknown that we started last time, by adding the three methods to the interface. An introduction to active template library atl 5 tenouk. This compensation may impact how and where products appear on this site including, for example, the order in which they appear. The code below will get the idispatch of an acdbobject or acdbobjectid, which can be passed to the above constructor. It correctly checks to make sure that the pointer isnt null before trying to convert the idispatch pointer to an irequest pointer.
If youre not using atl, then you need to change the ccomptr to lpunknown, and you have to call the iunknowns addref and release members beforeafter you use it. Whats the difference between ccomptr and ccomqiptr. Wrapper class for the itypeinfo interface method name vtable offset iunknown. The code used 3 atl features ccomptr smart pointer, manages addref and release automaticall ccomqiptr smart point with automatic queryinterface calls ccomvariant varient support need for paraenters for the dispatch interface you need to replace them with the raw api code. Ccomptrs constructor performs an addref on the pointer while the destructor. The idispatch interface performs its own release, so the code above calls release twice, the first time explicitly through the call dispatchrelease and the second. That is, you can use an instance of a smart pointer class in many of the places you normally use a pointer.
By continuing to use pastebin, you agree to our use of cookies as described in the cookies policy. As tlb files are not always provided to users, i have decided to use idispatch to find published methods. Mingw minimalist gnu for windows list mingwusers archives. Occasionally while using com, youll want to pass parameters to a method without any knowledge of the data types the method requires. Topics and sub topics for this tutorial are listed below.
You receive a null pointer when the queryinterface calls fail. A smart pointer is an object that behaves like a pointer. Iunknown is the root interface for all com objects. The automation idispatch interface allows a client. Comptr provides a much simpler syntax for doing queryinterface calls on com objects. We use cookies for various purposes including analytics. If the client calls function1, function2, or function3 on the interface, the client accesses those functions directly as it would for any other com interface. The idea is that all com objects offer a basic interface called iunknown, which has just three methods. It looks as though atl took a cue from mfc for implementing queryinterface, atl uses a lookup table just like mfcs. In other words, assignment followed by destruction has a net effect of zero on the pointer you assigned.
I also tried inheriting directly from iunknown, but still i never reached the breakpoint in my version of queryinterface. Variantarg rgvarg array of arguments dispid rgdispidnamedargs disp ids of named args. The windows mfc active template library atl information and. A nonnull owned object gets a release call upon the ccomptr. When you implement one or more userdefined interfaces in a class, visual basic provides an implementation of queryinterface that allows clients to move among interface references. However, it seems that sometimes smart pointers are too smart in particular, im referring to the secret queryinterface ing assignment operator discussed by jared parsons on his blog. But if you want to do that you can use queryinterface to get idispatch pointer but that is not converting you will be getting a new pointer. The following functions both do the same logical operations. Anyway, i guess what im looking for is confirmation that smart pointers arent the global way of dealing with addref and release. Addref and release are use to control the life time of an object. Addref public int addref getaddress public int getaddress queryinterface public int queryinterface guid riid, int ppvobject release public int release. When passing comptr variables to constructors, you usually want the new class to increase the reference count, which is handled automatically by assigning the raw pointer to a new comptr or by copying one comptr to another. Every time addref is called, the internal counter value is incremented in one, and the function returns the number of objects that are currently using the interface.
If the requested identifier is among those supported, addref is called and the this pointer is returned. Well the best way is to get your idispatch interface directly with its clsid. Ccomptr provides a specialization for idispatch that enables it to. Addref this method is called when the set operator is invoked and increments the target objects reference count. Once you have the pointer to iunknown you now have to ask for the actual interface that you would like to work with.
The ccomptr and ccomqiptr classes can help eliminate memory leaks by performing automatic reference counting. Ccomptr provides a specialization for dealing with the idispatch interface. Ccomptr provides a specialization for idispatch that enables it to store pointers to com automation components and invoke the methods on the interface by using late binding. The difference between assignment and attachment with atl. How to addref an out parameter idispatch when using smart. Once everyone is done with the object the reference count drops to zero, the object can be. Another way of putting a pointer into a ccomptr is with the attach operator. The iunknown interface id is defined as a guid with the value of 0000000000000000c000000000000046 a com components interfaces are required to exhibit the reflexive, symmetric, and transitive properties. Ccomptr is used for managing objects that surely support some interface. Queryinterface addref release interface iunknown operations. A visual basic object automatically implements queryinterface.
However, the second version may be less errorprone because it uses the ccomptr class. Queryinterface this method is used when resolving a late binding member resolution. Hi, if you want to find out all possible objects then you need a idispatch pointer to excel. However, when the client calls queryinterface for idispatch, which version of idispatch should the client get, iatlspaceship s dispatch interface or imotions dispatch interface. Stdmethodimp invokedispid dispidmember, refiid riid, lcid lcid, word wflags, dispparams pdispparams, variant pvarresult, excepinfo pexcepinfo, uint puargerr. In this case we want to work with idispatch, which is a dynamic interface that lets us figure out which methods to call at runtime. Errorchecking routine that performs manual lifetime management of a com.
The reflexive property refers to the ability for the queryinterface call on a given interface with the interfaces id to return the same instance of the interface. The idispatch interface performs its own release, so the code above calls release twice. Because smart pointers are typically automatic variables rather than dynamically allocated variables, they are automatically cleaned up when they go out of scope. To gaurantee correct functionality, iunknown methods are always the first entries in the vtable. Youll soon see a version of this function that calls queryinterface. The first time addref is called, an internal counter an integer value is set to one, and the object is created. Find answers to whats the difference between ccomptr and ccomqiptr.
Application which you can then use to obtain itypeinfo, itypelib pointers to enumerate all the stuff. Com programming idispatch, queryinterface, cocreateinstance, iunknown, gettickcount, itoa, atl control. The interface header also includes the dual attribute to indicate a dual interface. When the ccomptr is destructed, it will release the pointer, undoing the addref that was performed by the assignment operator. Ccomptr is a convenient smart pointer atl class to manage reference counting of com objects. Ccomptrencapsulates a com interface pointer by wrapping the addref and.
Notice that in the idl fragment, the syntax seems more standard. Oct 03, 2014 tips for debugging com addrefrelease leaks heejune atl com programming october 3, 2014 october 3, 2014 2 minutes in windows environment, adding an accessibility support to a program means youll have to do a lot of com coding. Release this method is called when the object is explicitley set to nothing and decrements the target objects reference count. Ccomqiptr is for cases when you want to call queryinterface in a convenient manner to know whether an interface is supported. The use of ccomptr and ccomqiptr simplifies the syntax of the application by reducing the calls to addref, release, and queryinterface sprinkled throughout the code. While its a very simple interface, compared to some of the others well get to later, it does highlight a number of interesting and important behaviors that the. A multiple inheritance based com framework codeproject. Having to remember to call addref and release instead of delete shouldnt be a big deal.
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