C++ default constructor definition: what do we call a constructor that has no parameters, or whose parameters all have default values?

Introduction / Context:
Default construction is ubiquitous in C++ because containers, arrays, and many APIs require the ability to create objects without supplying arguments. Understanding precisely what qualifies as a “default constructor” clarifies why certain code compiles—or fails—when zero-argument construction is attempted.

Given Data / Assumptions:

• A class may have multiple constructors with or without parameters.
• If a constructor can be called with no arguments, it is considered a default constructor.
• Parameters with default values count as “optional.”

Concept / Approach:

A default constructor is any constructor that can be invoked with no arguments. This includes a function with an empty parameter list and also a constructor where every parameter has a default value, allowing calls with zero arguments. A copy constructor is distinct; it takes a reference to another object of the same type and initializes from it. Therefore, “default constructor” is the correct term for the described case, not “copy constructor” and not “both.”

Step-by-Step Solution:

Verification / Alternative check:

Declare T(int x = 1); and invoke T(). This compiles, demonstrating that defaulted parameters still yield a default constructor. Removing defaults and leaving only T(int) breaks zero-argument construction, illustrating the definition’s boundary.

Why Other Options Are Wrong:

Copy constructor: not callable with zero arguments.

Both A and B: mixes distinct concepts.

None of these: incorrect since a well-known term exists.

Common Pitfalls:

• Assuming that declaring any constructor suppresses implicit default constructor generation entirely; rules depend on which constructors are declared.
• Confusing value-initialization and default-initialization details; both require an accessible default constructor.

Final Answer:

default constructor