When Should You Implement a User-Defined Copy Constructor in C ?

When is a User-Defined Copy Constructor Necessary?

The C compiler automatically generates a copy constructor for classes, which performs member-wise copying by default. However, in certain situations, we may need to define our own user-defined copy constructor.

Reasons for Defining a User-Defined Copy Constructor:

• Deep Copying: When the member variables of a class allocate dynamic memory that needs to be copied separately, member-wise copying is insufficient. In such cases, a user-defined copy constructor is necessary to perform deep copying, which creates a new copy of the dynamic memory for the object's member variables.

Examples:

Consider the following class that stores a character string:

<code class="cpp">class Class {
public:
    Class(const char* str);
    ~Class();
private:
    char* stored;
};</code>

With the default copy constructor, the stored member would only be copied by reference, leading to undefined behavior when one of the copies is destroyed. To prevent this, we define a user-defined copy constructor that performs deep copying:

<code class="cpp">Class::Class(const Class& another) {
    stored = new char[strlen(another.stored) + 1];
    strcpy(stored, another.stored);
}</code>

Furthermore, a user-defined copy constructor is also required for the assignment operator to perform deep copying correctly:

<code class="cpp">void Class::operator = (const Class& another) {
    char* temp = new char[strlen(another.stored) + 1];
    strcpy(temp, another.stored);
    delete[] stored;
    stored = temp;
}</code>

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