12: Memory Management

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Questions and Answers

What must be done in memory management for every new allocation?

Allocate additional memory

Copy the allocated memory

Free the allocated memory (correct)

Move the allocated memory

A stack allows insertion and removal of elements only at the bottom.

False

What is the primary function of the 'pop' method in a stack?

To delete the top-most element from the stack.

The data structure stack is essentially a linked list where elements can be inserted and removed only from the ______.

top Signup and view all the answers

Match the following methods with their descriptions:

push = Adds an element to the top of the stack pop = Removes the top-most element from the stack top = Returns the value of the top-most element empty = Checks if the stack is empty Signup and view all the answers

In the struct 'lnode', what type is the 'value' field?

int Signup and view all the answers

What is the purpose of the 'empty' method in the stack class?

To determine whether the stack has any elements. Signup and view all the answers

What is the purpose of the assignment operator in the stack class implementation?

To create a copy of another stack instance Signup and view all the answers

The Rule of Three states that if one of the constructor, destructor, or assignment operator is implemented, all three must be implemented.

True Signup and view all the answers

What happens to the local variable 'copy' when it goes out of scope after the swap in the assignment operator?

It is cleaned up, deleting the stack associated with 'copy'. Signup and view all the answers

The stack class needs a __________ to destruct instances that are not used anymore.

destructor Signup and view all the answers

Match the member functions of a C++ class with their primary function:

Constructor = Creates a new instance Destructor = Destroys an instance Copy Constructor = Initializes a new instance as a copy Assignment Operator = Assigns a copy of one instance to another Signup and view all the answers

What does the default constructor `stack() : topn(nullptr) {}` do?

Initializes topn with the null pointer Signup and view all the answers

The function `stack::empty()` returns true if the stack has at least one element.

False Signup and view all the answers

What is the purpose of the `top()` function in the stack implementation?

To return the top value of the stack while ensuring the stack is not empty. Signup and view all the answers

When calling push(4), a new node is created with value __ and the next pointer to the current top node.

4 Signup and view all the answers

What happens when the `pop()` function is called on an empty stack?

It throws an assertion error. Signup and view all the answers

The `topn` pointer is redirected to the next node after a `pop()` operation.

True Signup and view all the answers

What is the consequence of dereferencing a null pointer while using the `top()` function?

It leads to undefined behavior. Signup and view all the answers

The operation `topn = new lnode(value, topn);` in the `push()` method creates a new node with the value of __.

value Signup and view all the answers

What does copy construction in C++ refer to?

Initializing an object with another object of the same type Signup and view all the answers

If a copy constructor is not defined, the automatically-generated copy constructor will not be called.

False Signup and view all the answers

What is the signature of the copy assignment operator in C++?

T& T::operator=(const T& t) Signup and view all the answers

The copy constructor of a class T has the declaration T (const T& ______).

t Signup and view all the answers

Match the following concepts with their definitions:

Copy Constructor = Called when an object is initialized using another object of the same type Assignment Operator = Overloaded function for assigning values to an already declared object Deep Copy = Creating a new copy of an object including all its dynamic resources Shallow Copy = Copying the object's bit pattern without creating duplicates of dynamic resources Signup and view all the answers

When is the copy constructor called for a class object?

When an object is declared and initialized with another object of the same class Signup and view all the answers

What is the purpose of the clean_up_nodes function?

To clean up the nodes and prevent memory leaks Signup and view all the answers

The assignment operator should return a reference to the right-hand side object.

False Signup and view all the answers

What is the purpose of defining our own copy constructor?

To control how an object is copied, especially for dynamic resources. Signup and view all the answers

It is valid to directly call the destructor to clean up a stack's data.

False Signup and view all the answers

What does the assignment operator do in the context of stacks?

It makes the left operand a copy of the right operand, managing memory by cleaning up old data. Signup and view all the answers

The automatically-generated assignment operator corresponds to a member-wise ______.

assignment Signup and view all the answers

The copy-and-swap idiom is an elegant strategy to implement the assignment operator using the ________ constructor.

copy Signup and view all the answers

What happens if no assignment operator is declared for a class?

A default assignment operator is automatically generated Signup and view all the answers

Match the following functions with their description:

clean_up_nodes = Cleans up the nodes to prevent memory leaks ~stack = Destructor that calls clean_up_nodes operator= = Assignment operator that makes a copy of another stack copy_nodes = Creates a copy of nodes from another stack Signup and view all the answers

What does std::swap do in the context of the copy-and-swap idiom?

It exchanges the top node pointers of two stacks. Signup and view all the answers

The assignment operator requires a conditional check to avoid self-assignment.

True Signup and view all the answers

What happens to the local copy of a stack when it goes out of scope in the copy-and-swap idiom?

Its destructor is called, which cleans up its data. Signup and view all the answers

In the assignment operator, after cleaning up old data, the new data is copied from the right operand to the left operand using the ________ function.

copy_nodes Signup and view all the answers

What is the primary effect of using the delete operator on a dynamically allocated object?

The object is deconstructed and memory is released Signup and view all the answers

Every new allocation in dynamic memory management must have a corresponding delete operation.

True Signup and view all the answers

What is meant by 'dangling pointers'?

Pointers that reference memory locations that have been released. Signup and view all the answers

The function to remove the top element from a stack is called __.

pop Signup and view all the answers

Match each term with its correct definition:

new = Allocates memory for a new object delete = Deallocates memory for an object stack = A data structure that follows LIFO principle lnode = Node structure used in linked list implementation Signup and view all the answers

What may happen if you release an object more than once using delete?

It can lead to undefined behavior Signup and view all the answers

The stack’s destructor automatically deletes all its elements upon release.

True Signup and view all the answers

What is the role of the 'push' method in the stack implementation?

To add a new element to the top of the stack. Signup and view all the answers

The expression 'delete p;' in the pop() method is used to __.

release the memory for the top node Signup and view all the answers

When deleting an object, what does the delete operator NOT do?

Set the pointer to nullptr Signup and view all the answers

What is the role of the 'push' method in the stack class?

Adds an element to the top of the stack Signup and view all the answers

In the stack class, the 'empty()' method returns true if there are elements in the stack.

False Signup and view all the answers

What is the default value of the 'topn' pointer in the stack's constructor?

nullptr Signup and view all the answers

The ______ method in the stack class asserts that the stack is not empty before returning the top value.

top Signup and view all the answers

Match the stack methods with their descriptions:

push = Adds an element to the stack pop = Removes the top element from the stack top = Returns the top element of the stack empty = Checks if the stack has any elements Signup and view all the answers

Which statement about the 'new' operator in C++ is true?

It allocates memory for a new object and returns its pointer. Signup and view all the answers

A stack implemented with a linked list allows elements to be accessed from both ends.

False Signup and view all the answers

What happens in the stack when the 'pop()' method is called on an empty stack?

An error occurs or an assertion fails Signup and view all the answers

The 'next' pointer in the 'lnode' struct points to the ______ node in the linked list.

next Signup and view all the answers

In the given stack implementation, which operator will not function correctly if no assignment operator is defined?

The assignment operator Signup and view all the answers

Which of the following describes the purpose of the '+ operator=' in a class?

Allows assigning values to an already initialized object Signup and view all the answers

A default constructor is called only when a new object is created.

True Signup and view all the answers

What happens to dynamically allocated memory if delete is not called?

Memory leak occurs. Signup and view all the answers

The ________ function is called automatically when the lifetime of an object ends.

destructor Signup and view all the answers

Which statement about the destructor is true?

It is automatically called when the object's scope ends. Signup and view all the answers

Why should pointers to deleted objects be set to nullptr?

To prevent dangling pointers. Signup and view all the answers

The copy constructor and the assignment operator serve the same purpose in class management.

False Signup and view all the answers

When implementing a class that uses pointers, it is important to follow the Rule of ______.

Three Signup and view all the answers

What happens when a class does not declare a destructor?

An automatically generated destructor will be created. Signup and view all the answers

What is the primary purpose of the `operator=` function in the stack class?

To assign one stack object to another Signup and view all the answers

The Rule of Three states that if a class defines a destructor, it is optional to define a copy constructor and an assignment operator.

False Signup and view all the answers

What occurs when the number of `std::shared_ptr` references to an object reaches zero?

The object is automatically deleted. Signup and view all the answers

In the assignment operator, the method used to swap pointers is called ________.

std::swap Signup and view all the answers

Match the following components with their description:

Destructors = Responsible for cleanup of resources Copy Constructors = Create a copy of an object Assignment Operators = Assign values from one object to another Smart Pointers = Manage dynamic memory automatically Signup and view all the answers

What happens to an object when its `shared_ptr` count decreases to zero?

It is deleted automatically. Signup and view all the answers

The statement `if (this != &s)` checks for self-assignment in the assignment operator.

True Signup and view all the answers

What mechanism does C++ provide for memory management when using `std::shared_ptr`?

Reference counting. Signup and view all the answers

The ________ mechanism ensures that all necessary resource management functions are implemented for a class in C++.

Rule of Three Signup and view all the answers

In the assignment operator for the stack, what does the line `stack copy = s;` effectively do?

It initializes a new stack with existing elements. Signup and view all the answers

Study Notes

Introduction to Computer Science

Course offered by the Department of Computer Science, ETH Zurich
Course code: 252-0032, 252-0047, 252-0058
Fall 2024
Authors: Manuela Fischer and Felix Friedrich

Memory Management

Dynamic memory allocation is discussed.
Dynamic data structures (like stacks) require explicit memory management.
Correct memory management involves a delete for every new operation.
A stack is a fundamental data structure that allows insertion and removal of elements only from the top (LIFO – Last-In, First-Out).
Stacks are implemented as linked lists.

Basic Stack Functionality

A stack's functionality includes:
- push: Adds an element to the top.
- pop: Removes the top element.
- top(): Returns the top element (without removing it).
- empty(): Checks if the stack is empty.

Stack Implementation Details (Data Structure)

lnode struct (used to represent nodes in a stack):
- Contains value (data held by the node)
- Contains next (pointer to the next lnode in the sequence).
topn is a pointer to the top node in the stack; it is a member variable of the stack class

Removing Elements from Stack

pop() function removes the top element:
- A temporary pointer old_topn stores the top pointer
- topn is re-directed to the next element
- old_topn is deleted

Dynamic Memory Management

For every new, there must be a matching delete
Ignoring this rule leads to memory leaks.

Avoiding Memory Leaks in Stacks

A push() function allocates memory when an element is pushed onto the stack.
The pop() function should deallocate memory when an element is removed from the stack.
A temporary variable old_topn is used to store the top node before it's removed; allowing correct deletion
The destructor for the stack class should release allocated memory during destruction. This involves iterating through all nodes and deallocating each node.

Destructors

The destructor of the stack class is essential for releasing dynamically allocated memory when the stack goes out of scope.
It will loop through all the remaining nodes and recursively call delete on every remaining node.

Copy Assignment Operator (Overloading)

Using stack s2 = s1 creates a copy of the stack s1 in stack s2.
Overloading the = operator is crucial to make sure copies are independent, and memory leaks don't occur.
Deep-copy mechanisms are needed to create true independent copies, using the copy_nodes() function.
The clean_up_nodes() function is crucial to free nodes that are now orphaned by the assignment operator.

Rule of Three

The rule of three states that if a class requires a custom constructor, a destructor, or a copy assignment operator, it should also implement the other two.
Often, providing a custom copy constructor or assignment operator requires modifying the rest of the special member functions (the Rule of Three).

Shared Pointers

Shared pointers automatically manage memory.
They maintain a reference count to track how many pointers refer to an object.
When the reference count reaches zero, the object is automatically deleted/freed.
Use std::make_shared<T> to create shared pointers to custom data types (e.g., rational).
Shared pointers alleviate memory management by automatically deleting an object when the last shared pointer goes out of scope.
Example use (std::shared_ptr) given: std::shared_ptr<rational> sp1 = std::make_shared<rational>(3, 4);
Proper deletion is crucial with shared pointers (e.g., sp1 = nullptr;) to prevent lingering references and possible memory leaks when several shared pointers exist for the same object.

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Description

This quiz covers memory management concepts in computer science, focusing on dynamic memory allocation and the fundamentals of stack data structures. Participants will explore stack operations such as push and pop, along with the implementation details pertaining to memory management. Assess your understanding of these crucial programming concepts.

12: Memory Management

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Podcast

Questions and Answers

What must be done in memory management for every new allocation?

A stack allows insertion and removal of elements only at the bottom.

What is the primary function of the 'pop' method in a stack?

The data structure stack is essentially a linked list where elements can be inserted and removed only from the ______.

Match the following methods with their descriptions:

In the struct 'lnode', what type is the 'value' field?

What is the purpose of the 'empty' method in the stack class?

What is the purpose of the assignment operator in the stack class implementation?

The Rule of Three states that if one of the constructor, destructor, or assignment operator is implemented, all three must be implemented.

What happens to the local variable 'copy' when it goes out of scope after the swap in the assignment operator?

The stack class needs a __________ to destruct instances that are not used anymore.

Match the member functions of a C++ class with their primary function:

What does the default constructor stack() : topn(nullptr) {} do?

The function stack::empty() returns true if the stack has at least one element.

What is the purpose of the top() function in the stack implementation?

When calling push(4), a new node is created with value __ and the next pointer to the current top node.

What happens when the pop() function is called on an empty stack?

The topn pointer is redirected to the next node after a pop() operation.

What is the consequence of dereferencing a null pointer while using the top() function?

The operation topn = new lnode(value, topn); in the push() method creates a new node with the value of __.

What does copy construction in C++ refer to?

If a copy constructor is not defined, the automatically-generated copy constructor will not be called.

What is the signature of the copy assignment operator in C++?

The copy constructor of a class T has the declaration T (const T& ______).

Match the following concepts with their definitions:

When is the copy constructor called for a class object?

What is the purpose of the clean_up_nodes function?

The assignment operator should return a reference to the right-hand side object.

What is the purpose of defining our own copy constructor?

It is valid to directly call the destructor to clean up a stack's data.

What does the assignment operator do in the context of stacks?

The automatically-generated assignment operator corresponds to a member-wise ______.

The copy-and-swap idiom is an elegant strategy to implement the assignment operator using the ________ constructor.

What happens if no assignment operator is declared for a class?

Match the following functions with their description:

What does std::swap do in the context of the copy-and-swap idiom?

The assignment operator requires a conditional check to avoid self-assignment.

What happens to the local copy of a stack when it goes out of scope in the copy-and-swap idiom?

In the assignment operator, after cleaning up old data, the new data is copied from the right operand to the left operand using the ________ function.

What is the primary effect of using the delete operator on a dynamically allocated object?

Every new allocation in dynamic memory management must have a corresponding delete operation.

What is meant by 'dangling pointers'?

The function to remove the top element from a stack is called __.

Match each term with its correct definition:

What may happen if you release an object more than once using delete?

The stack’s destructor automatically deletes all its elements upon release.

What is the role of the 'push' method in the stack implementation?

The expression 'delete p;' in the pop() method is used to __.

When deleting an object, what does the delete operator NOT do?

What is the role of the 'push' method in the stack class?

In the stack class, the 'empty()' method returns true if there are elements in the stack.

What is the default value of the 'topn' pointer in the stack's constructor?

The ______ method in the stack class asserts that the stack is not empty before returning the top value.

Match the stack methods with their descriptions:

Which statement about the 'new' operator in C++ is true?

A stack implemented with a linked list allows elements to be accessed from both ends.

What happens in the stack when the 'pop()' method is called on an empty stack?

The 'next' pointer in the 'lnode' struct points to the ______ node in the linked list.

In the given stack implementation, which operator will not function correctly if no assignment operator is defined?

Which of the following describes the purpose of the '+ operator=' in a class?

A default constructor is called only when a new object is created.

What happens to dynamically allocated memory if delete is not called?

The ________ function is called automatically when the lifetime of an object ends.

Which statement about the destructor is true?

Why should pointers to deleted objects be set to nullptr?

The copy constructor and the assignment operator serve the same purpose in class management.

When implementing a class that uses pointers, it is important to follow the Rule of ______.

What happens when a class does not declare a destructor?

What is the primary purpose of the operator= function in the stack class?

The Rule of Three states that if a class defines a destructor, it is optional to define a copy constructor and an assignment operator.

What occurs when the number of std::shared_ptr references to an object reaches zero?

In the assignment operator, the method used to swap pointers is called ________.

Match the following components with their description:

What happens to an object when its shared_ptr count decreases to zero?

The statement if (this != &s) checks for self-assignment in the assignment operator.

What mechanism does C++ provide for memory management when using std::shared_ptr?

What does the default constructor `stack() : topn(nullptr) {}` do?

The function `stack::empty()` returns true if the stack has at least one element.

What is the purpose of the `top()` function in the stack implementation?

What happens when the `pop()` function is called on an empty stack?

The `topn` pointer is redirected to the next node after a `pop()` operation.

What is the consequence of dereferencing a null pointer while using the `top()` function?

The operation `topn = new lnode(value, topn);` in the `push()` method creates a new node with the value of __.

What is the primary purpose of the `operator=` function in the stack class?

What occurs when the number of `std::shared_ptr` references to an object reaches zero?

What happens to an object when its `shared_ptr` count decreases to zero?

The statement `if (this != &s)` checks for self-assignment in the assignment operator.

What mechanism does C++ provide for memory management when using `std::shared_ptr`?

In the assignment operator for the stack, what does the line `stack copy = s;` effectively do?