Some C++ Knowledge

What is the result of the following code snippet?

• The value of x is: 20

• The value of x is: 22

• The value of x is: undefined behavior - don't do this!

• None, because it won't compile

• It prints out a secret message saying "You're an amazing C++ wizard!"

Answer explanation

The correct answer is c) The value of x in this case leads to undefined behavior. This code snippet exhibits a sequence point violation, which results in undefined behavior according to the C++ standard.

Modifying and using x multiple times within a single expression without any sequencing points can yield unpredictable results. Therefore, it's best to avoid such constructs in your code.

Which of the following is an example of a C++ keyword?

• print

• function

• hula-loop

• public

Answer explanation

The correct answer is d) public. In C++, keywords are reserved words that have special meanings and purposes in the language. They cannot be used as identifiers or variable names.

What is the difference between stack and heap memory allocation in C++?

• Stack memory is used for static variables, while heap memory is used for dynamic variables

• Stack memory is managed automatically by the compiler, while heap memory requires manual management.

• Stack memory has limited size and scope, while heap memory has a larger size and can be accessed globally

• All of the above

What is the purpose of "perfect forwarding" in C++?

• It allows passing arguments to functions without unnecessary copies or moves

• It ensures that all function parameters are initialized with default values

• It enables automatic type inference for template functions

• It magically teleports your arguments to another dimension

Answer explanation

Perfect forwarding, achieved through the use of std::forward and rvalue references (&&), enables passing arguments from one function to another while preserving their value category (lvalue/rvalue). This technique helps optimize performance by avoiding redundant object copying or moving during argument transfer.

What does the acronym "RAII" stand for in C++ development?

• Really Awesome and Interesting Implementation

• Resource Allocation Is Intense Integration

• Random Access Inheritance Interface

• Resource Acquisition Is Initialization

Answer explanation

RAII is an important concept in C++ programming that ties resource acquisition and release to object lifetimes. It ensures that resources, such as memory or file handles, are properly managed by tying their lifetime to the lifespan of objects. When an object is created, resources are acquired within its constructor, and when the object goes out of scope or is destroyed, the destructor automatically releases those resources. This approach helps prevent leaks and guarantees proper cleanup.

What is metaprogramming in C++?

• Writing code that generates random numbers at compile-time.

• A technique to write programs that can modify their own source code.

• The process of creating programs that can analyze and transform themselves or other programs during compilation.

• Using macros extensively to generate complex code structures.

Answer explanation

Metaprogramming in C++ refers to the ability to write programs that perform analysis, transformations, or computations at compile-time. It involves leveraging template metaprogramming techniques, such as using templates, type traits, constexpr functions, and variadic templates. With metaprogramming, it becomes possible to perform actions like generating types dynamically based on specific conditions or performing computations during the compilation phase itself. This technique allows for powerful optimizations and flexibility within your C++ codebase.

What is one notable difference between C++11 and C++14?

• The addition of lambda expressions

• The introduction of the auto keyword for type inference

• The inclusion of the constexpr specifier for compile-time evaluation

• int value = 0b101010; 
  // Binary literal representing
  // decimal value 42

Answer explanation

One significant difference between C++11 and C++14 is the introduction of binary literals allow you to specify integral values using a binary representation directly within your code. This makes it easier to work with binary data or bit manipulation operations. Binary literals are prefixed with 0b or 0B, followed by a sequence of 0s and 1s.

In contrast, options A (lambda expressions), B (auto keyword), and C (constexpr) were introduced in C++11 itself. These additions brought powerful capabilities to the language that improve code expressiveness, enable type deduction, and allow compile-time evaluation.

What is one notable difference between C++14 and C++17?

• The introduction of the 'auto' keyword for type inference

• The inclusion of the 'constexpr if' statement for compile-time conditional evaluation

• The support for nested namespaces

• The addition of lambda capture expressions

Answer explanation

One significant difference between C++14 and C++17 is the introduction of the constexpr if statement in C++17.

This feature allows you to conditionally evaluate code at compile-time based on a constexpr condition. It provides more flexibility compared to traditional template-based techniques like SFINAE (Substitution Failure Is Not An Error). With constexpr if, you can write cleaner and more readable code that selectively executes different branches depending on compile-time conditions.

Options A (the auto keyword), C (nested namespaces), and D (lambda capture expressions) were introduced in previous versions, specifically with C++11.

Which of the following statements about C++ destructors is correct?

• Destructors are explicitly called by the programmer

• Destructors are used to allocate memory for objects

• Destructors have a return type specified

• Destructors are automatically called when an object goes out of scope or is deleted

Answer explanation

In C++, destructors are special member functions that are automatically invoked when an object goes out of scope, such as at the end of a block, or when an explicit delete operator is used to deallocate dynamically allocated memory.

Destructors play a crucial role in resource management and cleanup. They release any resources acquired by the object during its lifetime, such as deallocating dynamic memory, closing files, releasing locks, etc.

Option A is incorrect because destructors do not need to be explicitly called by the programmer; their invocation happens implicitly based on scoping rules and delete operations.

Option B is incorrect because constructors (not destructors) handle memory allocation for objects.

Option C is incorrect because destructors do not have a return type specified; they have no return value and cannot be overloaded with different return types like constructors can be overloaded with different parameter lists.

What happens if you change the return type of the main() method to double?

• The program will not compile

• The program will compile, but it won't execute

• The program will run successfully and print "Hello, World!"

• The universe collapses

Answer explanation

In C++, the main() function is required to have a return type of int. It serves as the entry point for your program and returns an exit status code to indicate its execution status. Changing the return type to anything other than int, such as double, would result in a compilation error.