In C , How are Class Members Initialized and Destroyed?

Order of Initialization and Destruction of Class Members

In C , the order of initialization and destruction of class members plays a crucial role in object lifetime management. This behavior is commonly referred to as the "constructor and destructor call order."

Member Initialization Order

The C standard specifies that member variables are initialized in the order they are declared within the class definition. This order ensures that base classes are initialized before derived classes and that non-static data members are initialized in the order they appear.

Member Destruction Order

The reverse order applies to member destruction. Destructors are called in the reverse order of initialization, with derived class destructors called before base class destructors and non-static data member destructors called in the reverse order of their declaration.

Example

Consider the following program:

#include <iostream>
using namespace std;

struct A
{
    A() { cout << "A::A" << endl; }
    ~A() { cout << "A::~" << endl; }
};

struct B
{
    B() { cout << "B::B" << endl; }
    ~B() { cout << "B::~" << endl; }
};

struct C
{
    C() { cout << "C::C" << endl; }
    ~C() { cout << "C::~" << endl; }
};

struct Aggregate
{
    A a;
    B b;
    C c;
};

int main()
{
    Aggregate a;
    return 0;
}

When executed, this program produces the following output:

A::A
B::B
C::C
C::~
B::~
A::~

As expected, the members of Aggregate are initialized in the order A, B, then C, and their destructors are called in the reverse order.

Therefore, yes, C guarantees that members are initialized in the order of declaration and destroyed in reverse order for both class members and aggregate types.

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