Dynamic Object creation in MFC

Question

Dynamic Object creation in MFC

Roshni Bhaskaran 1

MFC internally uses CreateObject function to create class objects dynamically.

I was wondering as to what is the purpose of this feature.

We create objects dynamically using the new keyword in C++. What additional purpose does Dynamic Object creation of CObject class provide? Why was it there in the first place?

David Lowndes 4,726 Reputation points

2021-05-24T12:59:15.317+00:00

I believe MFC's design predates modern (even relatively old) C++ facilities such as RTTI, so some things were faked in a manner that was achievable in compilers at the time.
RLWA32 49,536 Reputation points

2021-05-24T13:06:16.733+00:00

In the absence of time travel its a little kinder to say "implemented" rather than "faked". :)
David Lowndes 4,726 Reputation points

2021-05-24T13:13:00.347+00:00

Yeah, "implemented" sounds better :)
Viorel 122.6K Reputation points

2021-05-24T17:10:15.253+00:00

Using something like CRuntimeClass::FromName(“some class name”)->CreateObject(), you can create an object based on its class name (a string). This is useful, for example, when you parse some binary or text file (XML, JSON), that describes the data. Do you know how to do it in modern C++ without artifices?
Roshni Bhaskaran 1 Reputation point

2021-05-25T02:12:31.707+00:00

No, I don't...

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David Lowndes 4,726 Reputation points

2021-05-24T12:59:15.317+00:00

I believe MFC's design predates modern (even relatively old) C++ facilities such as RTTI, so some things were faked in a manner that was achievable in compilers at the time.
RLWA32 49,536 Reputation points

2021-05-24T13:06:16.733+00:00

In the absence of time travel its a little kinder to say "implemented" rather than "faked". :)
David Lowndes 4,726 Reputation points

2021-05-24T13:13:00.347+00:00

Yeah, "implemented" sounds better :)
Viorel 122.6K Reputation points

2021-05-24T17:10:15.253+00:00

Using something like CRuntimeClass::FromName(“some class name”)->CreateObject(), you can create an object based on its class name (a string). This is useful, for example, when you parse some binary or text file (XML, JSON), that describes the data. Do you know how to do it in modern C++ without artifices?
Roshni Bhaskaran 1 Reputation point

2021-05-25T02:12:31.707+00:00

No, I don't...

Answer 1

Jeanine Zhang-MSFT 11,356 Microsoft External Staff

Hi

MFC internally uses CreateObject function to create class objects dynamically.I was wondering as to what is the purpose of this feature.

I suggest you could refer to the Doc: Run-Time Object Model Services

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.

Best Regards,

Jeanine

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Roshni Bhaskaran 1 Reputation point

2021-05-25T02:10:10.57+00:00

I went through the link shared by you. But still, my question persists - "framework needs to create them dynamically" - why can't this be done using the new keyword??
Jeanine Zhang-MSFT 11,356 Reputation points Microsoft External Staff

2021-05-25T07:13:54.873+00:00

@Roshni Bhaskaran

Each class derived from CObject is associated with a CRuntimeClass structure that you can use to obtain information about an object or its base class at run time. We should call CRuntimeClass::CreateObject to dynamically create the specified class during run time. For the Release version of the library, CObject::operator new does an optimal memory allocation in a manner similar to malloc.

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Dynamic Object creation in MFC

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