Windows ole component

Feedback will be sent to Microsoft: By pressing the submit button, your feedback will be used to improve Microsoft products and services. Privacy policy. The OLE DB Service Component Manager compares the properties specified by the consumer to the properties supported by the provider to determine whether individual service components could be used to satisfy extended functionality requested by the consumer.

For example, if an application requests a scrollable cursor and the provider only supports a forward-only cursor, the Service Component Manager uses the Client Cursor Engine service component to provide scrollable functionality.

This is a key solution to the problem of versioning, and is a fundamental requirement for achieving a component software market. COM additionally provides for robust versioning because COM interfaces are immutable, and COM components continue to support old interfaces even while adding new functionality through additional interfaces.

This guarantees backwards compatibility as components are upgraded. Other proposed system object models generally allow developers to change existing interfaces, leading ultimately to versioning problems as components are upgraded.

This freedom in other object models to change interfaces may appear on the surface to handle versioning, but in practice it does not work. For example, if version-checking is done only at object creation time, subsequent users of an instantiated object can easily fail because the object is of the right type but the wrong version. Per-call version-checking is too expensive to even contemplate!

Fast and simple object interaction. Once a client establishes a connection to a COM component, calls to that COM component's services interface functions are simply indirect functions calls through two memory pointers. As a result, the performance overhead of interacting with an in-process COM component an COM component that is in the same address space as the calling code is negligible.

In addition, using multiple interfaces per object is efficient because the cost of negotiating interfaces via QueryInterface is done in groups of functions instead of one function at a time.

Interface reuse. Design experience suggests that there are many sets of operations that are useful across a broad range of components. For example, it is commonly useful to provide or use a set of functions for reading or writing streams of bytes.

This not only allows for code reuse, but by reusing interfaces, the programmer learns the interface once and can apply it throughout many different applications. A key point is that the caller makes this call exactly as it would for an object in the same process. The binary standard enables COM to perform inter-process and cross-network function calls transparently. Although there is, of course, more overhead in making a remote procedure call, no special code is necessary in the client to differentiate an in-process object from an out-of-process object.

This means that as long as the client is written from the start to handle RPC exceptions, all objects in-process, cross-process, and remote are available to clients in a uniform, transparent fashion.

Microsoft will be providing a distributed version of COM that will require no modification to existing components in order to gain distributed capabilities. In other words, programmers are completely isolated from networking issues, and components shipped today will operate in a distributed fashion when this future version of COM is released.

Programming language independence. Any programming language that can create structures of pointers and explicitly or implicitly call functions through pointers can create and use COM components. COM components can be implemented in a number of different programming languages and used from clients that are written using completely different programming languages. Again, this is because COM, unlike an object-oriented programming language, represents a binary object standard, not a source code standard.

COM uses globally unique identifiers GUIDs , which are bit integers that are guaranteed to be unique in the universe across space and time, to identify every interface and every COM component class. Human-readable names are assigned only for convenience and are locally scoped.

This helps ensure that COM components do not accidentally connect to the "wrong" component, interface, or method, even in networks with millions of COM components. Microsoft supplies a tool uuidgen that automatically generates GUIDs. Through the use of defines, developers don't need to be exposed to the actual bit GUID.

The GUIDs are embedded in the component binary itself and are used by the COM system dynamically at bind time to ensure that no false connections are made between components.

COM defines one special interface, IUnknown , to implement some essential functionality. Figure 6 is a graphical representation of IUnknown.

Figure 6. The IUnknown interface. AddRef and Release are simple reference counting methods. While the COM component's reference count is non-zero it must remain in memory; when the reference count becomes zero, the COM component can safely unload itself, because no other components hold references to it. QueryInterface is the mechanism that allows clients to dynamically discover at run time whether or not an interface is supported by a COM component; at the same time, it is the mechanism that a client uses to get an interface pointer from a COM component.

When an application wants to use some function of a COM component, it calls that object's QueryInterface , requesting a pointer to the interface that implements the desired function.

If the COM component supports that interface, it will return the appropriate interface pointer and a success code. If the COM component doesn't support the requested interface, it will return an error value. The application will then examine the return code; if successful, it will use the interface pointer to access the desired method.

If the QueryInterface failed, the application will take some other action, letting the user know that the desired method is not available. The following example shows a call to QueryInterface on the PhoneBook component. We are asking this component, "Do you support the ILookup interface? Note that AddRef is not explicitly called in this case because the QueryInterface implementation increments the reference count before it returns an interface pointer.

The COM Library provides the ability to make IUnknown calls across processes; it also encapsulates all the "legwork" associated with launching components and establishing connections between components.

COM uses the object's IClassFactory to ask the class factory to create an instance of the COM component, and sends a pointer to the requested interface back to the calling application. The calling application neither knows nor cares where the server application is run; it just uses the returned interface pointer to communicate with the newly created COM component.

To summarize, COM defines several basic fundamentals that provide the underpinnings of the object model. The binary standard allows components written in different languages to call each other's functions.

Interfaces are logical groups of related functions--functions that together provide some well-defined capability. IUnknown is the interface that COM defines to allow components to control their own lifespan and to dynamically determine another component's capabilities. A COM component implements IUnknown to control its lifespan and to provide access to the interfaces it supports.

A COM component does not provide direct access to its data. GUIDs provide a unique identifier for each class and interface, thereby preventing naming conflicts. And finally, the COM Library is implemented as part of the operating system, and provides the "legwork" associated with finding and launching COM components. Now that we have a good understanding of COM's fundamental pieces, let's look at how these pieces fit together to enable component software.

COM addresses the four basic problems associated with component software:. Additionally, COM provides a high-performance architecture to meet the requirements of a commercial component market. These are provided by COM's use of vtables to define a binary interface standard for method calling between components. A good versioning mechanism allows one system component to be updated without requiring updates to all the other components in the system. The COM design completely eliminates the need for things like version repositories or central management of component versions.

For more information, click the following article number to view the article in the Microsoft Knowledge Base:. Certificate auto-enrollment may not function correctly. Edit the Registry Important This section, method, or task contains steps that tell you how to modify the registry. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base: How to back up and restore the registry in Windows Start Registry Editor.

Restart the operating system for the changes to take effect. EXE Run Dcomcnfg. Open the Computers folder. Type the computer name. Right-click the computer name, and then click Properties. Click the Default Properties tab. For more information, click the following article number to view the article in the Microsoft Knowledge Base: Description of the Microsoft Windows registry.

Need more help? Download and install any pending updates then restart. Make sure the latest Service Pack for Office is installed. How satisfied are you with this reply? Thanks for your feedback, it helps us improve the site. In reply to Andre for Directly's post on April 1, I recommend you uninstall Office then reinstall it using compatibility mode for Windows 7. OK, I will do what you recommend if it is the only advice. Keep in mind though, Windows 10 is making significant changes every 6 months that might break compatibility with older applications.

Also Office was lauched in June , thats almost 10 years ago. With support officially ending support next year, then Microsoft will start to wind down support on newer releases. In reply to Andre for Directly's post on April 2, Hi Andre, thank you for your answers. EXE Which version of Windows 10 is currently installed?