Declare a fixed-length array in nested classes

Question

I have a class A that has a nested class B. Class A will create n (runtime parameter) of class B.

In constructor A, after the calculations that need to be performed at runtime, I calculate the size, say, s.

Now each class B will contain an array of size s.

However, I am not allowed to use .cpp files, and all work must be done in the header files.

This means, as far as I understand, that I can not use this approach (c static):

class B {

static const int s;
int a[s];

};

So, I decided to use enum, but I could not get it to work (even with enum classC ++ 11). The idea is that you are doing something like:

class B {

enum { s = 50 };
int a[s];

};

but I don't know suntil runtime.

, std::vector dynamic allocation.

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2) , B, ( )

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Answer 1

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Answer 2

. -, : . . , , . -, , ++.

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#include <vector>
#include <cstddef>

class A {
    private:
        class B {
            friend A;
            B(size_t n) : array(n) {}
            std::vector<int> array;
        };
    public:
        // Initialize b_member based on some computation.
        A(int i) : b_member(i + 2), b_ptr_member(new B(i + 3)) {}
        ~A() { delete b_ptr_member; }
    private:
        B b_member;
        B *b_ptr_member;
};

int main() {
    A a(10);
}

Answer 3

++. . std::vector, std::vector::shrink_to_fit .:

class B {
  ...
  std::vector<int> a;
  ...
};

Answer 4

: std::vector. :

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