Destructor role in C++ - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a destructor in a C++ class.

C++

class MyClass {
public:
    ~[1]();
};

Drag options to blanks, or click blank then click option'

Adelete

BmyClass

CDestructor

DMyClass

Attempts:

3 left

💡 Hint

Common Mistakes

Using a different name than the class for the destructor.

Omitting the tilde (~) before the destructor name.

The destructor has the same name as the class, preceded by a tilde (~).

2fill in blank

medium

Complete the code to define a destructor that prints a message when called.

C++

MyClass::~MyClass() {
    std::cout << [1] << std::endl;
}

Drag options to blanks, or click blank then click option'

ADestructor_called

BDestructor called

C"Destructor called"

Ddestructor

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting the quotes around the message string.

Using a variable name instead of a string literal.

The message must be a string literal enclosed in double quotes.

3fill in blank

hard

Fix the error in the destructor declaration.

C++

class MyClass {
public:
    ~MyClass[1];
};

Drag options to blanks, or click blank then click option'

A{}

B()

C;

D[]

Attempts:

3 left

💡 Hint

Common Mistakes

Omitting parentheses in the destructor declaration.

Using braces {} instead of parentheses ().

The destructor declaration must include empty parentheses ().

4fill in blank

hard

Fill both blanks to complete the destructor definition that frees a dynamically allocated array.

C++

class MyClass {
    int* data;
public:
    MyClass() { data = new int[10]; }
    ~MyClass() {
        [1] data;
        data = [2];
    }
};

Drag options to blanks, or click blank then click option'

Adelete[]

Bnullptr

C0

Ddelete

Attempts:

3 left

💡 Hint

Common Mistakes

Using delete instead of delete[] for arrays.

Not setting pointer to nullptr after deletion.

Use delete[] to free arrays and set pointer to nullptr to avoid dangling pointers.

5fill in blank

hard

Fill all three blanks to complete the destructor that closes a file and resets the pointer.

C++

class FileHandler {
    FILE* file;
public:
    FileHandler(const char* filename) {
        file = fopen(filename, "r");
    }
    ~FileHandler() {
        if ([1] != nullptr) {
            [2](file);
            file = [3];
        }
    }
};

Drag options to blanks, or click blank then click option'

Afile

Bfclose

Cnullptr

Dopen

Attempts:

3 left

💡 Hint

Common Mistakes

Not checking if file pointer is nullptr before closing.

Using wrong function to close the file.

Not resetting pointer after closing.

Check if file is not nullptr, then close it with fclose, and reset pointer to nullptr.

Practice

1. What is the main role of a destructor in C++?

easy

A. To clean up resources when an object is destroyed

B. To create new objects

C. To initialize variables

D. To overload operators

Solution

1. Step 1: Understand the purpose of a destructor

   A destructor is a special function that runs when an object is destroyed to free resources like memory or files.

2. Step 2: Compare with other options

   Creating objects, initializing variables, and overloading operators are not roles of destructors.

3. Final Answer:

   To clean up resources when an object is destroyed -> Option A

4. Quick Check:

   Destructor role = cleanup [OK]

Hint: Destructor always cleans up when object ends [OK]

Common Mistakes:

• Confusing destructor with constructor
• Thinking destructor creates objects
• Believing destructor initializes variables

2. Which of the following is the correct syntax for a destructor in a class named Car?

easy

A. Car~() {}

B. void ~Car() {}

C. ~Car() {}

D. void Car() {}

Solution

1. Step 1: Recall destructor syntax

   A destructor has the same name as the class with a tilde (~) prefix and no return type.

2. Step 2: Check each option

   ~Car() {} matches the correct syntax. void ~Car() {} wrongly includes 'void'. Car~() {} has wrong order. void Car() {} lacks tilde and looks like a constructor.

3. Final Answer:

   ~Car() {} -> Option C

4. Quick Check:

   Destructor syntax = ~ClassName() [OK]

Hint: Destructor name = ~ + class name, no return type [OK]

Common Mistakes:

• Adding return type to destructor
• Placing tilde after class name
• Confusing destructor with constructor syntax

3. What will be the output of this C++ code?

class Box {
public:
  Box() { std::cout << "Created\n"; }
  ~Box() { std::cout << "Destroyed\n"; }
};

int main() {
  Box b;
  return 0;
}

medium

A. Destroyed\nCreated\n

B. Created\nDestroyed\n

C. Created\n

D. No output

Solution

1. Step 1: Trace object creation

   When b is created, constructor prints "Created".

2. Step 2: Trace object destruction

   At end of main(), b is destroyed, destructor prints "Destroyed".

3. Final Answer:

   Created\nDestroyed\n -> Option B

4. Quick Check:

   Constructor then destructor output [OK]

Hint: Constructor runs first, destructor runs last [OK]

Common Mistakes:

• Assuming destructor runs before constructor
• Expecting no output
• Confusing order of prints

4. Identify the error in this destructor code:

class Sample {
public:
  ~Sample(int x) { }
};

medium

A. Destructor cannot have parameters

B. Destructor must return int

C. Destructor name should not have ~

D. Destructor must be static

Solution

1. Step 1: Check destructor parameters

   Destructors cannot have parameters; they must have empty parentheses.

2. Step 2: Verify other rules

   Destructor has no return type, must have ~ prefix, and cannot be static.

3. Final Answer:

   Destructor cannot have parameters -> Option A

4. Quick Check:

   Destructor params = none [OK]

Hint: Destructor always has empty parentheses [OK]

Common Mistakes:

• Adding parameters to destructor
• Adding return type
• Removing ~ from destructor name

5. Consider a class FileHandler that opens a file in its constructor. Which is the best way to ensure the file is closed properly when the object is no longer needed?

hard

A. Do nothing; files close automatically when program ends

B. Manually call a close method before deleting the object

C. Rely on the operating system to close the file automatically

D. Write a destructor that closes the file

Solution

1. Step 1: Understand resource management

   Files opened by an object should be closed when the object is destroyed to avoid resource leaks.

2. Step 2: Use destructor for cleanup

   Destructor runs automatically when object ends, so closing the file there ensures proper cleanup.

3. Final Answer:

   Write a destructor that closes the file -> Option D

4. Quick Check:

   Destructor cleans resources automatically [OK]

Hint: Use destructor to free resources automatically [OK]

Common Mistakes:

• Forgetting to close files causing leaks
• Relying on manual close calls
• Assuming OS always cleans up immediately