Section 9 : Exception Handling

Question 1

What is the difference between C and C++ memory allocation?

Answer 1

Uses malloc() and free(), no constructor/destructor support.

int* p = (int*) malloc(sizeof(int));
free(p);

Uses new and delete, which also call constructors/destructors.
int* p = new int;
delete p;

Question 2

How does error handling differ between C and C++?

Answer 2

C: Manual error checks using return values.

C++: Uses structured exception handling (try, throw, catch).

Question 3

What are the three keywords used in C++ exception handling?

Answer 3

try: Marks a block of code to watch.

throw: Raises an exception.

catch: Handles the thrown exception.

Question 4

What happens when an exception is thrown in a try block?

Answer 4

Execution jumps to the first matching catch block. Remaining code in try is skipped.

Question 5

How are multiple catch blocks evaluated?

Answer 5

Top to bottom. The first matching block is executed. The default handler catch(…) should always come last.

Question 6

Where should you handle exceptions?

Answer 6

Inside the function where the error happens. Don’t delegate low-level checks to main().

Question 7

How do you re-throw an exception in nested try-catch?

Answer 7

Use throw; in an inner catch to pass the exception to an outer try block.

Question 8

What does throw(int) after a function signature mean?

Answer 8

It means the function can only throw exceptions of type int. (Note: deprecated in modern C++.)

Question 9

How do custom exception classes work in C++?

Answer 9

You inherit from std::exception and override what():

class DivisionByZero : public std::exception {
const char* what() const throw() { return “Division by zero”; }
};

Question 10

Why use exception classes instead of error codes?

Answer 10

Cleaner design using polymorphism. Easier to manage with a single catch block.

Question 11

What is the advantage of catch (const std::exception&)?

Answer 11

It can catch any exception derived from std::exception, thanks to polymorphism.

Question 12

What are some common standard exceptions in C++?

Answer 12

std::bad_alloc (allocation failure)

std::bad_cast (invalid cast)

std::runtime_error, std::out_of_range, etc.