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Run-Time Object Model Services

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The latest version of this topic can be found at Run-Time Object Model Services.

The classes CObject and CRuntimeClass encapsulate several object services, including access to run-time class information, serialization, and dynamic object creation. All classes derived from CObject inherit this functionality.

Access to run-time class information enables you to determine information about an object's class at run time. The ability to determine the class of an object at run time is useful when you need extra type-checking of function arguments and when you must write special-purpose code based on the class of an object. Run-time class information is not supported directly by the C++ language.

Serialization is the process of writing or reading an object's contents to or from a file. You can use serialization to store an object's contents even after the application exits. The object can then be read from the file when the application is restarted. Such data objects are said to be "persistent."

Dynamic object creation enables you to create an object of a specified class at run time. For example, document, view, and frame objects must support dynamic creation because the framework needs to create them dynamically.

The following table lists the MFC macros that support run-time class information, serialization, and dynamic creation.

For more information on these run-time object services and serialization, see the article CObject Class: Accessing Run-Time Class Information.

Run-Time Object Model Services Macros

DECLARE_DYNAMIC Enables access to run-time class information (must be used in the class declaration).
DECLARE_DYNCREATE Enables dynamic creation and access to run-time class information (must be used in the class declaration).
DECLARE_SERIAL Enables serialization and access to run-time class information (must be used in the class declaration).
IMPLEMENT_DYNAMIC Enables access to run-time class information (must be used in the class implementation).
IMPLEMENT_DYNCREATE Enables dynamic creation and access to run-time information (must be used in the class implementation).
IMPLEMENT_SERIAL Permits serialization and access to run-time class information (must be used in the class implementation).
RUNTIME_CLASS Returns the CRuntimeClass structure that corresponds to the named class.

OLE frequently requires the dynamic creation of objects at run time. For example, an OLE server application must be able to create OLE items dynamically in response to a request from a client. Similarly, an automation server must be able to create items in response to requests from automation clients.

The Microsoft Foundation Class Library provides two macros specific to OLE.

Dynamic Creation of OLE Objects

DECLARE_OLECREATE Enables objects to be created through OLE automation.
IMPLEMENT_OLECREATE Enables objects to be created by the OLE system.

DECLARE_DYNAMIC

Adds the ability to access run-time information about an object's class when deriving a class from CObject.

DECLARE_DYNAMIC
(class_name)

Parameters

class_name
The actual name of the class.

Remarks

Add the DECLARE_DYNAMIC macro to the header (.h) module for the class, then include that module in all .cpp modules that need access to objects of this class.

If you use the DECLARE_ DYNAMIC and IMPLEMENT_DYNAMIC macros as described, you can then use the RUNTIME_CLASS macro and the CObject::IsKindOf function to determine the class of your objects at run time.

If DECLARE_DYNAMIC is included in the class declaration, then IMPLEMENT_DYNAMIC must be included in the class implementation.

For more information on the DECLARE_DYNAMIC macro, see CObject Class Topics.

Example

See the example for IMPLEMENT_DYNAMIC.

DECLARE_DYNCREATE

Enables objects of CObject-derived classes to be created dynamically at run time.

DECLARE_DYNCREATE
(class_name)

Parameters

class_name
The actual name of the class.

Remarks

The framework uses this ability to create new objects dynamically. For example, the new view created when you open a new document. Document, view, and frame classes should support dynamic creation because the framework needs to create them dynamically.

Add the DECLARE_DYNCREATE macro in the .h module for the class, then include that module in all .cpp modules that need access to objects of this class.

If DECLARE_DYNCREATE is included in the class declaration, then IMPLEMENT_DYNCREATE must be included in the class implementation.

For more information on the DECLARE_DYNCREATE macro, see CObject Class Topics.

Note

The DECLARE_DYNCREATE macro includes all the functionality of DECLARE_DYNAMIC.

Example

See the example for IMPLEMENT_DYNCREATE.

DECLARE_SERIAL

Generates the C++ header code necessary for a CObject-derived class that can be serialized.

DECLARE_SERIAL
(class_name)

Parameters

class_name
The actual name of the class.

Remarks

Serialization is the process of writing or reading the contents of an object to and from a file.

Use the DECLARE_SERIAL macro in an .h module, and then include that module in all .cpp modules that need access to objects of this class.

If DECLARE_SERIAL is included in the class declaration, then IMPLEMENT_SERIAL must be included in the class implementation.

The DECLARE_SERIAL macro includes all the functionality of DECLARE_DYNAMIC and DECLARE_DYNCREATE.

You can use the AFX_API macro to automatically export the CArchive extraction operator for classes that use the DECLARE_SERIAL and IMPLEMENT_SERIAL macros. Bracket the class declarations (located in the .h file) with the following code:

#undef AFX_API
#define AFX_API AFX_EXT_CLASS

// <your class declarations here>

#undef AFX_API
#define AFX_API

For more information on the DECLARE_SERIAL macro, see CObject Class Topics.

Example

class CAge : public CObject
{
public:
    void Serialize(CArchive& ar);
    DECLARE_SERIAL(CAge)

    // remainder of class declaration omitted

IMPLEMENT_DYNAMIC

Generates the C++ code necessary for a dynamic CObject-derived class with run-time access to the class name and position within the hierarchy.

IMPLEMENT_DYNAMIC
(class_name, base_class_name)

Parameters

class_name
The actual name of the class.

base_class_name
The name of the base class.

Remarks

Use the IMPLEMENT_DYNAMIC macro in a .cpp module, and then link the resulting object code only once.

For more information, see CObject Class Topics.

Example

class CPerson : public CObject 
{
   DECLARE_DYNAMIC( CPerson )

   // other declarations
};

IMPLEMENT_DYNAMIC( CPerson, CObject )

IMPLEMENT_DYNCREATE

Enables objects of CObject-derived classes to be created dynamically at run time when used with the DECLARE_DYNCREATE macro.

IMPLEMENT_DYNCREATE
(class_name, base_class_name)

Parameters

class_name
The actual name of the class.

base_class_name
The actual name of the base class.

Remarks

The framework uses this ability to create new objects dynamically, for example, when it reads an object from disk during serialization. Add the IMPLEMENT_DYNCREATE macro in the class implementation file. For more information, see CObject Class Topics.

If you use the DECLARE_DYNCREATE and IMPLEMENT_DYNCREATE macros, you can then use the RUNTIME_CLASS macro and the CObject::IsKindOf member function to determine the class of your objects at run time.

If DECLARE_DYNCREATE is included in the class declaration, then IMPLEMENT_DYNCREATE must be included in the class implementation.

Note that this macro definition will invoke the default constructor for your class. If a non-trivial constructor is explicitly implemented by the class, it must also explicitly implement the default constructor as well. The default constructor can be added to the class's private or protected member sections to prevent it from being called from outside the class implementation.

Example

class CMyDynCreateObj : public CObject
{
     int m_Num;
public:
     DECLARE_DYNCREATE(CMyDynCreateObj)
     CMyDynCreateObj(int Num) { m_Num = Num; }
private:
     CMyDynCreateObj() { m_Num = 0; }  // provide default constructor only for 
                                       // dynamic creation 
};

IMPLEMENT_DYNCREATE(CMyDynCreateObj, CObject)

IMPLEMENT_SERIAL

Generates the C++ code necessary for a dynamic CObject-derived class with run-time access to the class name and position within the hierarchy.

IMPLEMENT_SERIAL
(class_name, base_class_name, wSchema)

Parameters

class_name
The actual name of the class.

base_class_name
The name of the base class.

wSchema
A UINT "version number" that will be encoded in the archive to enable a deserializing program to identify and handle data created by earlier program versions. The class schema number must not be –1.

Remarks

Use the IMPLEMENT_SERIAL macro in a .cpp module; then link the resulting object code only once.

You can use the AFX_API macro to automatically export the CArchive extraction operator for classes that use the DECLARE_SERIAL and IMPLEMENT_SERIAL macros. Bracket the class declarations (located in the .h file) with the following code:

#undef AFX_API
#define AFX_API AFX_EXT_CLASS

// <your class declarations here>

#undef AFX_API
#define AFX_API

For more information, see the CObject Class Topics.

Example

IMPLEMENT_SERIAL(CAge, CObject, VERSIONABLE_SCHEMA | 2)

RUNTIME_CLASS

Gets the run-time class structure from the name of a C++ class.

RUNTIME_CLASS
(class_name)

Parameters

class_name
The actual name of the class (not enclosed in quotation marks).

Remarks

RUNTIME_CLASS returns a pointer to a CRuntimeClass structure for the class specified by class_name. Only CObject-derived classes declared with DECLARE_DYNAMIC, DECLARE_DYNCREATE, or DECLARE_SERIAL will return pointers to a CRuntimeClass structure.

For more information, see CObject Class Topics.

Example

      CRuntimeClass* prt = RUNTIME_CLASS(CAge);
      ASSERT(strcmp(prt->m_lpszClassName, "CAge") == 0);

DECLARE_OLECREATE

Enables objects of CCmdTarget-derived classes to be created through OLE automation.

DECLARE_OLECREATE
(class_name)

Parameters

class_name
The actual name of the class.

Remarks

This macro enables other OLE-enabled applications to create objects of this type.

Add the DECLARE_OLECREATE macro in the .h module for the class, and then include that module in all .cpp modules that need access to objects of this class.

If DECLARE_OLECREATE is included in the class declaration, then IMPLEMENT_OLECREATE must be included in the class implementation. A class declaration using DECLARE_OLECREATE must also use DECLARE_DYNCREATE or DECLARE_SERIAL.

IMPLEMENT_OLECREATE

Either this macro or IMPLEMENT_OLECREATE_FLAGS must appear in the implementation file for any class that uses DECLARE_OLECREATE.

IMPLEMENT_OLECREATE(class_name, external_name, l, w1, w2, b1, b2, b3, b4, b5, b6, b7, b8)

Parameters

class_name
The actual name of the class.

external_name
The object name exposed to other applications (enclosed in quotation marks).

l, w1, w2, b1, b2, b3, b4, b5, b6, b7, b8
Components of the class's CLSID.

Remarks

Note

If you use IMPLEMENT_OLECREATE, by default, you support only the single threading model. If you use IMPLEMENT_OLECREATE_FLAGS, you can specify which threading model your object supports by using the nFlags parameter.

The external name is the identifier exposed to other applications. Client applications use the external name to request an object of this class from an automation server.

The OLE class ID is a unique 128-bit identifier for the object. It consists of one long, two WORDs, and eight BYTEs, as represented by l, w1, w2, and b1 through b8 in the syntax description. The Application Wizard and code wizards create unique OLE class IDs for you as required.

See Also

Macros and Globals