Why Must C Copy Constructors Use Reference Parameters?

The Necessity of Reference Parameter in Copy Constructors in C

When working with objects in C , it becomes crucial to understand the role of copy constructors, and one essential aspect is passing the parameter by reference. Let's explore the reason why this is mandatory.

Passing Parameter by Reference vs. by Value

In C , parameters can be passed to functions in two ways: by reference or by value. By reference means the function accesses the original variable directly, while by value creates a copy of the original variable for use within the function.

Infinite Recursion with Value Parameter

If the copy constructor were to accept its parameter by value, it would lead to an infinite loop. To understand why, consider the following pseudocode:

class MyClass {
    int value;
public:
    MyClass(int v) : value(v) {}  // Copy constructor with parameter passed by value
};

If we call MyClass myObject(5);, the copy constructor will be invoked. However, since the parameter is passed by value, a copy of the original integer is created. To initialize this copy, we need to call the copy constructor again. This leads to an infinite recursion because the copy constructor keeps calling itself without making any progress.

Avoiding Recursion with Reference Parameter

Passing the parameter by reference breaks the infinite recursion. When the parameter is passed by reference, the copy constructor directly operates on the original variable, avoiding the need to create a copy and call the copy constructor recursively.

class MyClass {
    int value;
public:
    MyClass(int& v) : value(v) {}  // Copy constructor with parameter passed by reference
};

With the parameter passed by reference, the myObject variable is directly initialized with the value 5 without invoking the copy constructor multiple times.

Conclusion

In summary, the copy constructor's parameter must be passed by reference in C to avoid falling into an infinite recursion. By passing the parameter by reference, the copy constructor can modify the original variable directly, ensuring correct object initialization and preventing unnecessary duplication of work.

The above is the detailed content of Why Must C Copy Constructors Use Reference Parameters?. For more information, please follow other related articles on the PHP Chinese website!