Skip to main content

Virtual Table *_vptr , VTBL, C++

VTBL or VPTR nothing but virtual table and virtual pointer in C++.

It gets created when we create function with virtual keyword. As soon as we create the virtual function in a class A table gets created behind the code.

BaseClass
{
virtual void function1(){...}
}

ChildClass : public BaseClass
{
virtual void function1(){...}// method overridden.
}

When we override method that is create another version of function in derived class ChildClass in above case then the *_vptrvirtual void function1(){...}// method overridden. gets created for BaseClass.

So VTBL Of Base Class has entry for function1 and Child class will be pointing to that function. *_vptr is nothing but the pointer to function.

Note: ones the virtual keyword is introduced all the upcoming functions are considered as virtual.

ChildClass: public BaseClass
{
virtual void function1(){...}// method overridden.
void function2(){}
}

In above case function2 also considered as virtual.

BaseClass will not be pointing to any of Child Class functions and ChildClass will be pointing to all the virtual functions whose entry is in VTBL of baseclass as soon as the object of the base class instantiated or the method is overridden.

Tags : pointer, virtual, C++, function pointer,VTBL, VPTR, Function overriding , polymorphism

Comments

Popular posts from this blog

Dotnet, .Net 3.5, 2.0, C# Interview Questions

Few questions on dotnet, C# 2.0, 3.5 On Object oriented concepts 1)What is inheritance with e.g 2)What is polymorphism -function overloading -Function overriding -virtual keyword use -Static keyword and use -Abstract classes -Interface -Object 3)What is threading and how do we use in realtime application(cognizant) 4)What is threadpooling, lock, monitor(write code sample) 5)Architecture of current project 6)Session state, diffrent types of state management. 7)What is Application_Start, how it works. 8)Type of authentication in asp.net 9)How to configure ASP.NET application. 10) What is Impersonation. 11) What is WebService, WSDL, UDDI, Discovery, asmx files. 12) How to implement WebService and use it. 13) When to use WebServices. 14) WPF, how to implement(BOA) 15) Testing concvepts. 16) Test attributes 17) Flow of Automation Test Method execution 18) Features of dotnet 3.5 19) CLR, garbage collection 20) Finally block 21) Manifest, Metadata, MSIL 22) Assemblies, Type of assemblies, str...

Linux SMB write performance With Simple Tips

SMB write performance can be increased by Tuning the buffer cache. The secret to good performance is to keep as much of the data in memory for as long as is possible. Writing to the disk is the slowest part of any filesystem. If you know that the filesystem will be heavily used, then you can tune this process for Linux Samba. writing out dirty blocks to the disk until the filesystem buffer cache is 80 percent full (80). default is 40%, source = http://tldp.org/LDP/solrhe/Securing-Optimizing-Linux-RH-Edition-v1.3/chap29sec287.html by writing echo 80 > /proc/sys/vm/dirty_ratio I am getting around 2MB increase while write operation, tested in Xp. I have tried with this single option, as the ref source is for linux 2.2 and we are using 2.6 kernel. we can try out Linux General Optimization suggested at http://tldp.org/LDP/solrhe/Securing-Optimizing-Linux-RH-Edition-v1.3/gen-optim.html Tried with smb.conf, I am getting around 1MB gain while read and write. socket options = TCP_NODELAY I...

The Linux Foundation Free Training Program at linuxfoundation

The Linux Foundation Training Program is: * For the Community, by the Community. The Linux Foundation is building the program with its Technical Advisory Board to ensure the content, instructors and classes are the top quality available. * Technically the most advanced. Since the Linux Foundation works directly with community developers, it can cover features and advances in Linux before commercial companies. * Connected. The Linux Foundation has unfettered access to the leading developers and companies in the Linux ecosystem and will use these connections to best position attendees for success. For example, attendees can attend the exclusive, invite-only Collaboration Summit where they can forge connections beneficial to their career. * Real World. The Linux Foundation training courses all have hands on components and a highly rigorous curriculum of programming or administration exercises. Graduates will be well equipped to master Linux programming and system administr...