Podcast
Questions and Answers
What is the purpose of the 'push' function in the stack class?
What is the purpose of the 'push' function in the stack class?
The 'pop' function can be called on an empty stack without causing an error.
The 'pop' function can be called on an empty stack without causing an error.
False
What does the 'top' function return in the stack class?
What does the 'top' function return in the stack class?
the value of the top most element
In a linked list, each node is represented by a struct called ______.
In a linked list, each node is represented by a struct called ______.
Signup and view all the answers
Match the functions with their descriptions:
Match the functions with their descriptions:
Signup and view all the answers
What happens when you dereference a dangling pointer?
What happens when you dereference a dangling pointer?
Signup and view all the answers
Releasing an object more than once using delete is a safe practice.
Releasing an object more than once using delete is a safe practice.
Signup and view all the answers
What is a dangling pointer?
What is a dangling pointer?
Signup and view all the answers
The function pop()
in a stack implementation removes the ______ item from the top of the stack.
The function pop()
in a stack implementation removes the ______ item from the top of the stack.
Signup and view all the answers
Match the following operations with their effects:
Match the following operations with their effects:
Signup and view all the answers
What is the purpose of the assert statement in the pop()
function?
What is the purpose of the assert statement in the pop()
function?
Signup and view all the answers
What will happen to the variable 'topn' when the pop()
function is called?
What will happen to the variable 'topn' when the pop()
function is called?
Signup and view all the answers
The statement int nominator = (*t).denominator();
is valid after delete s;
.
The statement int nominator = (*t).denominator();
is valid after delete s;
.
Signup and view all the answers
What happens to objects created with new when delete is called?
What happens to objects created with new when delete is called?
Signup and view all the answers
Each new statement must have a matching delete statement to prevent memory leakage.
Each new statement must have a matching delete statement to prevent memory leakage.
Signup and view all the answers
What is the consequence of not pairing every new with a delete statement?
What is the consequence of not pairing every new with a delete statement?
Signup and view all the answers
The delete operator does not set the pointer to ________ after deletion.
The delete operator does not set the pointer to ________ after deletion.
Signup and view all the answers
Match the following outcomes to their corresponding actions:
Match the following outcomes to their corresponding actions:
Signup and view all the answers
What might happen if a pointer pointing to a deleted object is accessed?
What might happen if a pointer pointing to a deleted object is accessed?
Signup and view all the answers
After a delete operation, all pointers to the deleted object become invalid.
After a delete operation, all pointers to the deleted object become invalid.
Signup and view all the answers
What is the guideline for dynamic memory management regarding new and delete?
What is the guideline for dynamic memory management regarding new and delete?
Signup and view all the answers
What does the empty()
function in the stack class indicate?
What does the empty()
function in the stack class indicate?
Signup and view all the answers
The top()
function can be called even if the stack is empty.
The top()
function can be called even if the stack is empty.
Signup and view all the answers
What keyword is used to ensure that the stack is not empty in the top()
method?
What keyword is used to ensure that the stack is not empty in the top()
method?
Signup and view all the answers
In the default constructor for the stack class, topn
is initialized to ____.
In the default constructor for the stack class, topn
is initialized to ____.
Signup and view all the answers
Match the stack methods with their descriptions:
Match the stack methods with their descriptions:
Signup and view all the answers
What is the return type of the top()
method?
What is the return type of the top()
method?
Signup and view all the answers
The topn
variable in the stack class points to the last element added to the stack.
The topn
variable in the stack class points to the last element added to the stack.
Signup and view all the answers
What happens when the 'push' method is called with an integer value?
What happens when the 'push' method is called with an integer value?
Signup and view all the answers
The 'delete' operator releases memory for objects created with 'new'.
The 'delete' operator releases memory for objects created with 'new'.
Signup and view all the answers
What does the 'new' operator do when creating an object of type T?
What does the 'new' operator do when creating an object of type T?
Signup and view all the answers
What is the effect of calling 'delete' on an object created with 'new'?
What is the effect of calling 'delete' on an object created with 'new'?
Signup and view all the answers
The top of the stack will contain the value __ after calling 'push(4)'.
The top of the stack will contain the value __ after calling 'push(4)'.
Signup and view all the answers
Match the following expressions with their effects:
Match the following expressions with their effects:
Signup and view all the answers
What type of storage duration do objects created with 'new' have?
What type of storage duration do objects created with 'new' have?
Signup and view all the answers
The 'topn' pointer remains the same after a 'push' operation.
The 'topn' pointer remains the same after a 'push' operation.
Signup and view all the answers
What does the 'matching constructor' do when an object is created?
What does the 'matching constructor' do when an object is created?
Signup and view all the answers
Study Notes
Memory Management
- Dynamic data structures, like
our_list
, were allocated memory last week, but not released. This resulted in the absence of functions to remove elements. - Today's focus is correcting memory management using
new
anddelete
, aided by the dynamic data structurestack
.
Goal: Class Stack with Memory Management
- The goal is to create a
stack
class that manages memory.-
push(int value)
: Pushes an element onto the stack. -
pop()
: Removes the top element from the stack (presuming it's not empty). -
top() const
: Returns the value of the top element (presuming the stack is not empty). -
empty() const
: Returns true if the stack is empty, false otherwise.
-
Recall the Linked List
- Review the
lnode
structure, which represents an element in a linked list with an integer value and a pointer to the next node. -
lnode(int v, lnode* n)
is a constructor definition.
Stack = Pointer to the Top Element
- The
stack
now utilizes a pointer (topn
) to the top element of the linked list.
Empty Stack
- The default constructor for the
stack
class,stack() : topn(nullptr) { }
, initializes the top pointer tonullptr
. - The
empty()
function returnstrue
whentopn
isnullptr
, and false otherwise. - The
top()
function asserts (!empty()) before returning the current top node's value viatopn->value
.
The new Expression
- The
new
operator allocates memory for a new object of typeT
. - The effect is allocating new memory and initializes the object using the matching constructor.
- The value returned is the address of the new object of type
T
(type: pointerT*
).
The delete Expression
- Objects allocated with
new
have dynamic storage duration and exist until explicitly deleted usingdelete
. - The
delete
operator deallocates the memory associated with a pointer of typeT*
that was previously created withnew
. It deconstructs (cleans up) the object and does not set the pointer tonullptr
. A common programming error involves reusing a pointer that has already been deleted.
Who is Born Must Die...
- An important guideline for dynamic memory management: every
new
should have a correspondingdelete
. - Non-compliance can lead to memory leaks by leaving objects unused but in memory.
Careful with new and delete!
- Be mindful of using
new
anddelete
to prevent memory leaks. Especially, avoid referencing a previously deleted object, otherwise it can lead to dangling pointers.
Stack Continued: pop()
- The
pop()
function removes and deletes the top element by updating thetopn
pointer and handling the possiblenullptr
case.
Zombie Elements
- Local stack variables (
s1
) can potentially exist even after leaving or exiting scope. - Memory that those stack variables referenced may not be deallocated immediately after exiting the scope of use, causing a memory leak.
The Destructor
- The destructor (~T()) is a unique class member function that runs automatically when the memory duration of a an object ends: explicitly when
delete
is called on an object of typeT*
or when the enclosing scope finishes. - If no destructor is defined, one is automatically generated, handling the deallocation of members, like pointers in our stack.
Using a Destructor, It Works
- The destructor is called when a stack is about to be deallocated, deleting each object. This avoids memory leaks that could arise with a stack variable from going out of scope.
Stack Done?
- Demonstrates basic stack operation, but if a copy of a stack is made, both stacks point to the same memory.
- This means modifying one might cause modifications in the other as well.
What Has Gone Wrong?
- Copy initialization makes both stacks point to the same memory block. Subsequent actions like
pop()
on one stack will unintentionally affect the other.
The Actual Problem
- Copying a stack with dynamic memory allocation copies only the pointer to the top node, not the node's content. This means both stacks point to the same memory location. This leads to unpredictable result as either variable can modify node data directly.
Possible Solutions
- Deep copy: Create a complete duplicate of the stack data.
- No copies: Prohibit the copying of the stack, thereby eliminating the shared memory issue.
- Shared data structure: Employ a solution that manages the shared data structure properly, thereby preventing shared access to memory.
The Copy Constructor
- A class's copy constructor is invoked when creating a new object by initializing it with an existing object of the same type.
- It automatically duplicates the data of an object to avoid accidental modification of the original.
- If no copy constructor is defined, the compiler will generate one, implementing member-wise initialization (copying of the individual elements).
It Works with a Copy Constructor
- This provides a solution for creating true copies of the stacks, resulting in a separate copy and preventing overlapping memory usage.
- The copy constructor is a method that correctly handles copying the dynamic memory from one object to another.
Initialization ≠ Assignment!
- Initialization (e.g.,
stack s2 = s1;
) and assignment (e.g.,s2 = s1;
) of a stack object behave differently. The first is the copy constructor and the second necessitates an assignment operator.
The Assignment Operator
- The assignment operator
operator=
provides an efficient mechanism to assign one stack (RHS) to another (LHS). - It's a member function handling the proper assignment of a stack to another.
- The operator copies data and handles self-assignment, ensuring memory is correctly allocated and freed.
Smart Pointers
- Smart pointers are pointers that, with additional routines, also take care of memory management.
-
std::shared_ptr
: It counts references to an object. It deletes the object only when the number of references drops to zero. So, if several pointers refer to the same object, they manage the memory automatically to avoid accidental memory leaks.
Shared Pointers: Example
- Demonstrates use of
std::make_shared
and handling shared pointers similarly to regular pointers in code. - A
shared_ptr
is used to create objects that are shared amongst several variables. This ensures that the memory is released properly when the last variable referencing that memory is deallocated.
Application: Workshop
- Workers share tools in a workshop, and the tools should be automatically returned when not in use.
Workshop: 1st Try
-
tool
struct: Holds a tool's name. -
worker
struct: Manages tools ("hammer", etc.), with ause
method for acquiring them and arelease
method for returning them (sharing is not correct).
Workshop: Attempt with Pointer
- Using pointers (
tool_ptr
) improves sharing but introduces manual deallocation issues. - Incorrect sharing leads to multiple copies.
Workshop: Solution with Shared Pointers
- Implement tool sharing via
std::shared_ptr
from the C++ standard library. - This approach ensures correct memory management by removing a particular pointer from the reference count when no longer in use. This automatically frees memory when no one holds the pointer.
Memory management independent of C++
- Garbage collection (GC) in other languages automatically reclaims unused memory.
- C++ provides explicit dynamic memory management.
- C++'s way of managing memory provides more control, but requires developers to be mindful in handling pointers to avoid memory leaks and potential crashes.
Studying That Suits You
Use AI to generate personalized quizzes and flashcards to suit your learning preferences.
Related Documents
Description
Test your knowledge on stack operations, memory management, and pointer concepts in data structures. This quiz covers essential functions such as 'push', 'pop', and the importance of memory release in programming. Perfect for students studying data structures and algorithms.