Using sizeof () class with empty base class in GCC

[Alfiee]

Hey dude, before doing any risky solution I must suggest you the basic thing in this problem. The sizeof() method of the gcc will be help to get the size of the class or variable. Then I think you need to just retry this code. There might be possible that this will work and the problem is solved. The other way is to mention that both VC++ and GCC output. This will generate sizeof(Vector4) = 16 result. Then try this and see the result.

[Author]

This type of different output generate because a difference in those compilers of the system. This compiler will be generating vtables. This vtables is an virtual table and it provide the size of the class or the variable to the sizeof() class. Hence you need to check this result on the different compiler. You also check this on the different system. This will be helping to you for solving such programming problem. The C++ standard compilers will also good choice.

[Dwarner]

If you clearly think this code then you observe that it happen only when both Vector4 AND Matrix4x4 inherit from Base. Does really you need inheritance in this situation. The heterogeneous Base* container of Vector4s and Matrix4x4s help to also alternatively do this task. The Object Oriented approach is generally damaging to performance in this case. The better way is using one of the open source graphics math libraries. This is help to solve the problem.

[Ronchi]

I think you need to do some different thing in this problem. Hence use the helper functions to 'Base' class. This helper function was able to access from both the child classes. You need to remove the base class in any 'Vector4' or 'Matrix4x4' class for fixing this problem. This will be help to 'Base class' will remain empty of member variables. I hope this work and the program gives correct result. Then try this and it might work in your case.

[Shreevats]

A programmer should in no way think what the sizeof() a type is other than sizeof(char). It is guaranteed to be 1. By default this is based on the application on sizeof(type). A compiler is free to create the sizeof() of any user-defined type. A user-defined struct or class can have padding or special alignment that would reason unusual results. Even the same compiler may be generate the different result. Then use this and it help to solve the problem.

[Villiers]

GCC C++ follows standard rules such as class EmptyBase {}; --> sizeof(EmptyBase) == 1. The other thing is to be any number of empty-bases class will plot to 0 in the struct offset. This is also unique types. Non empty-base parent’s class is declared with only padding for alignment. If the derived class first member right away follows empty-bases then it not derives. This will be help to you for solving such kind of troubles.

[Jacques25]

Maybe you didn’t know but all empty-base classes will come out to zero effective storage in its derived class. You have not need to concern the current offset if not go after by another empty-base class. This is the main rule in the gcc sizeof () method. You need to follow this rule. This will be providing the restriction over such kind of problems. If you follow this rule then this problem are not occur in this programming.