Avoid calling constructor of member variable

Question

I have the following C++-class:

// Header-File
class A
{
    public:
    A();

    private:
    B m_B;
    C m_C;
};

// cpp-File
A::A()
: m_B(1)
{
    m_B.doSom         


        

Answer 1

How about using technique described in this QA?

Prevent calls to default constructor for an array inside class

std::aligned_storage::type

---

Or, you also can consider using of union. AFAIK, unions will be initialized only with first named member's constructor.

For example,

union
{
   uint8_t _nothing = 0; 
   C c;
};

According to the standard mentioned in the QA, c will be zero-initialized, and its constructor will not be called.