[Microsoft]'s '''[http://www.microsoft.com/com/%|%Component Object Model]''',
or '''COM''', a component of [Microsoft Windows%|%Windows], enables software
components to communicate.



** Disambiguation **

   [Serial Ports on Windows]:   [MS-DOS]-style serial-line devices are also called COM ports




** Description **


Many popular [Microsoft Windows%|%Windows] applications expose a
[http://msdn.microsoft.com/en-us/library/windows/desktop/aa367809%28v=vs.85%29.aspx%|%COM
automation interface], which allows external programs to launch and control
them.  

Alex Martelli:  "COM-related technologies seem mostly pretty good, except for
the little detail that they're often huge, rambling, and full of redundancies
and pitfalls -- this goes for the object model of WMI just as well as for those
of MS Office applications."

At various times, [steveo], [stever], [CL], and others have worked on [DCOM].

[[Explain relation between COM and [WSH].]]



** Example: ProgID **

The starting point to an application's COM automation interface is through its
programmatic identifier (ProgID).  

Here are a few example ProgID's, any of which might be used in, for instance,
[tcom] with


======
set application [::tcom::ref createobject $ProgID]


Netscape.Network.1 [http://developer.netscape.com/docs/manuals/communicator/OLE/ole2net.htm]
FrontPage.Editor.Document
Word.Document (note that WordPad is ''not'' a COM server)
InternetExplorer.Application
Excel.Application
Excel.Application.8
PDF.PdfCtrl.1
Word.Application
DSOleFile.PropertyReader
======


** Finding Available COM Objects **

In [http://groups.google.com/d/msg/comp.lang.tcl/Q_-Schxqh5U/MMTjeIJNbgQJ%|%How
do you find all ActiveX servers?], [comp.lang.tcl], 2001-10-19, [Chin Huang]
provides the following code to search the Windows registry for available COM
objects, and prints their ProgID:

======
package require registry

set classesRootKey "HKEY_CLASSES_ROOT\\CLSID"
foreach clsid [registry keys $classesRootKey] {
    set clsidKey "$classesRootKey\\$clsid"
    set progIdSubKey [registry keys $clsidKey "VersionIndependentProgID"]
    if {[llength $progIdSubKey] > 0} {
        set progId [registry get "$clsidKey\\$progIdSubKey" ""]
        puts $progId
    }
}
======


** COM Constants **

One of the eternal puzzles of COM work is how to find the right constants.
Mark Hammond packaged up his insight on COM's constants into a [Python] module
called
[http://docs.activestate.com/activepython/2.7/pywin32/html/com/win32com/HTML/QuickStartClientCom.html#UsingComConstants%|%win32com.clients.constants].
Presumably we could, given enough motivation, do the same for Tcl, or at least
render the code into human-readable direction.

The section titled '''How to Obtain Built-In Constant Values for an Office
Application''' on the page
[How one discovers the API for a COM-exporting application] explains how to do this using [tcom].



**  Structured Storage **

COM
[http://msdn.microsoft.com/en-us/library/windows/desktop/aa380369%28v=vs.85%29.aspx%|%Structured
Storage] provides file and data persistence in COM by handling a single file as
a structured collection of objects known as storages and streams. [Pat Thoyts]'
[http://www.patthoyts.tk/tclstorage/%|%tclstorage] provides access to
Structured Storage from Tcl. 


Pat also has an "OLE Application automation" [http://www.patthoyts.tk/index.html#autonotepad]

** See Also **


   [http://en.wikipedia.org/wiki/Component_object_model%|%Wikipedia]:   

   [http://www.magicsplat.com/book/com.html%|%COM chapter]:    from [BOOK Tcl Programming for Windows]

   [TclScript]:   COM-aware

   [COMet]:   a COM Explorer for Tcl, which relies on [tcom], facilities discovery and interactive programming of COM objects.

   [COM Tree]:   another COM inspector

   [COM Events]:   

   [COM gateway extension]:   

   [COM on! - a tiny web browser]:   

   [COSH]:    
   
   [OLE Object Viewer]:   

   [optcl]:   Another Tcl interface to COM 

   [TclBridge]:   allows [Tcl] to call COM objects and vice-versa.  Very powerful, lots of options.

   [tcom]:   included in recent [ActiveTcl] releases, offers both client and server COM functionality.

   [TWAPI COM support]:   describes [TWAPI]'s client side COM capabilities.

<<categories>> Glossary | Windows | COM