What Determines the Initialization Order of Non-Static Data Members in C ?

Initialization Order of Non-Static Data Members

In C , the order of initialization of non-static data members in a class is determined by the order in which they are declared within the class definition. This is specified in section 12.6.2 of the C Standard.

The standard states that "nonstatic data members shall be initialized in the order they were declared in the class definition." This order applies regardless of the order of any member initializers that may be present in the class definition.

Consider the following class definition:

class A {};
class B {};
class X
{
    A a;
    B b;
};

When the constructor for class X is called, the data members a and b will be initialized in the order they appear in the class definition. This means that the constructor for class A will be called before the constructor for class B.

The standard specifies this order to ensure that base and member subobjects are destroyed in the reverse order of initialization. This is important to prevent dangling pointers and other memory management issues.

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