3. Create a COM component manually 1. From Project Creation to registration In this process, we will complete three steps: Create the DLL entry function, define the interface file, and implement the registration function. 1.1 create a Win32 DLL Project Create a Win32 DLL project named mathcom.
In step 2 of the wizard, select the "A smiple DLL project" option. Of course, if you select an empty project, complete the definition of dllmain by yourself. 1.2 define interface file Generate an interface file named mathcom. IDL. Add the file to the project you just created. After the correct settings, if there is no compilation error, four
| File Name |
Function |
| Mathcom. h |
Interface header file. If you want to declare or define an interface, use this file |
| Mathcom_ I .c |
Interfaces, class objects, and libraries are defined. This file is introduced only when guid-related things are used. This file can only be introduced once throughout the project, otherwise, a duplicate definition error occurs. |
| Mathcom_p.c |
Used for stubs and Proxies |
| Dlldata. c |
Unknown |
1.3 added the registration function COM must be registered and logged out. 1.3.1 Add a mathcom. Def File The def file is a module definition file ). It allows the lead symbol to be suffixed with different import symbols. // Mathcom. Def File
; Mathcom. Def: Declares the module parameters.
Conclusion 1.5 The following files should be included in our project:
| File Name |
Function |
| Stdafx. h and stdafx. cpp |
Pre-compiled files |
| Mathcom. cpp |
DLL entry function and other important function definitions |
| Mathcom. Def |
Module definition file |
| Mathcom. IDL |
Interface definition file (four files should be compiled after 1.2) |
Now, my so-called COM has implemented the registration and logout functions. If the following "regsvr32" is executed under the command line or "run" menu
Register this COM component with the absolute path + mathcom. dll. After executing this command, check the hkey_classes_root/CLSID entry of the Registry.
Whether the 3bcfe27e-c88d-rjc-8c94-f5f7b97e7841 exists (God bless ). For example, Run "regsvr32-u absolute path + mathcom. dll" in the same method as above, and then check the registry.
In fact, the generated DLL is not a COM component. Haha !!! Because it neither implements dllgetclassobject () nor implements either of the ismiplemath and iadvancedmath interfaces.
Let's move on !!! 2. Implement ismiplemath, iadvancedmath, and dllgetclassobject () 2.1 implement ismiplemath and iadvancedmath Interfaces Let's modify the original cmath class to implement the ismiplemath interface and iadvancedmath interface.
The modification is as follows: 1) math. h file
/* @ ** # --- 2003-10-29 21:33:44 (tulip )---#**@
# Include "interface. H "*/
# Include "mathcom. H" // newly added to replace the above 2.2 general process of calling COM components
- 1) Use coinitialize Sequence Function (client) for com library Initialization)
- 2) Activate COM (client)
- 3) use the registry key to transfer the corresponding DLL to the com Library (COM library)
- 4) Call the dllgetclassobject () function (COM component) in the COM component)
- 5) it is not necessary to return the interface pointer (COM Library) through the class factory.
2.3 dllgetclassobject () Implementation
Add the following statements to mathcom. cpp, #include "math.h"
#include "MathCOM_i.c" Modify dllgetclassobject () in mathcom. cpp to the following:
2.4 Client Next we will write a client program to test this COM.
Create an empty Win32 console project named testmathcom and add it to mathcom workspace.
Add a file named main. cpp to the testmathcom project. The content of this file is as follows: // Main. cpp File
# Include <windows. h>
# Include "../mathcom. H" // note the path here
# Include "../mathcom_ I .c" // note the path here
# Include <iostream>
Using namespace STD;
Conclusion 2.5 Now we should have 2 projects and 8 files, as shown below:
| Engineering |
File |
Function |
| Mathcom |
Stdafx. h and stdafx. cpp |
Pre-compiled files |
| |
Mathcom. cpp |
DLL entry function and other important function definitions |
| |
Mathcom. Def |
Module definition file |
| |
Mathcom. IDL |
Interface definition file (four files should be compiled after 1.2) |
| |
Math. h and math. cpp |
Ismiplemath, iadvancedmath interface implementation class |
| Testmathcom |
Main. cpp |
Mathcom client, used to test the mathcom component |
In this section, we have completed a practical COM component that is close to the complete. We have completed the client of this COM component. If you have already created a com instance, you may find that the client in this section does not use cocreateinstance () to create a com instance, that's because we haven't implemented the iclassfactory interface in this COM component (this interface is implemented in the next part ).
Through this example, I hope you can understand the following points:
- 1) For more information about the role of dllgetclassobject (), see the general procedure of calling COM components. Also, set the breakpoint to the dllgetclassobject () function, take a closer look at his implementation (without implementing the iclassfactory Interface) and his input parameters.
- 2)
Why is cogetclassobject () used to create COM instances instead of cocreateinstance () in this client program. You
You can try to use cocreateinstance () to create cmath and see what is the first parameter of dllgetclassobject?
- 3) implementing the iclassfactory interface is not necessary, but it should be said to be necessary (for how to implement it, see the next chapter)
- 4) The implementation of dllregisterserver () and dllunregisterserver () should be mastered.
- 5) The client needs the files when calling the COM component (as long as the two files generated by the IDL file)
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