Question

I want to write a class in C++ in which one of the parameter is a bitset<size>.
I want to give the facility to vary this “size” for any object of that class but should be constant for that object.

If I make a variable const int size; and initialize it in the constructor, then it does not compile because to writiting bitset<size> would require size to be static which would make it same for all objects of the class.

Is there any other method than making a class template and passing the size as classname<size>?

thanks but.. but this makes this Foo class objects whenever used as composition (object as data member)… would it be necessary to again make that class template. I made a class and Passed a (#define BIT_SIZE 16 to Foo bits;) it is giving compile errors undefined reference to Foo<16>::Foo(). where Foo() is the constructor. I thought it should work because that is also compile time. and i just wanted to make only size BIT_SIZE bits. should i make my “next level” class template ?? it can be that these errors were because of other mistakes. but i checked that again and again.

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yes sir i have implemented that and but included the header files and not cpp files ………. when i changed these to cpp files … multiple declaration error came. i am working on linux ubuntu .. when i took these files to dev_cpp in windows that worked . may be because compiler did that automatically what i need to do. so what is that i need to do.

Answer 1

No, there is no other method, because the code for actual instantiation for bitset<N> is generated at compile time, so you have no possibility to delay providing its size until runtime. You have to use the non-type template parameter.

If it was possible, the creators of standard C++ library would have done this and it would be possible to provide the size for bitset at runtime, right?

Using another bit set implementation is an option.