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Questions and Answers
What is the primary benefit of using STL containers in C++?
What is the primary benefit of using STL containers in C++?
Which of the following operations can be performed on a vector?
Which of the following operations can be performed on a vector?
What is the result of calling v.size() on an empty vector?
What is the result of calling v.size() on an empty vector?
In a vector, how is the last element accessed?
In a vector, how is the last element accessed?
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Which method would you use to determine if a vector is empty?
Which method would you use to determine if a vector is empty?
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What is a key property of a vector compared to a list in C++ STL containers?
What is a key property of a vector compared to a list in C++ STL containers?
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Which constructor creates a list initialized with ten elements of the value 4.22?
Which constructor creates a list initialized with ten elements of the value 4.22?
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Which of the following methods is guaranteed to operate in constant time for all C++ STL containers?
Which of the following methods is guaranteed to operate in constant time for all C++ STL containers?
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Which constructor would copy the elements from another container defined by the iterators [b,e)?
Which constructor would copy the elements from another container defined by the iterators [b,e)?
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What type of time complexity does the remove operation of a vector exhibit when removing elements not at the end?
What type of time complexity does the remove operation of a vector exhibit when removing elements not at the end?
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Study Notes
Introduction to STL Containers
- STL containers are used to efficiently manage collections of objects.
- They streamline complex tasks by providing useful functions and data structures.
- Containers ensure consistency across different object types.
- Template classes define containers independently from the data type within.
- Each container type optimizes access and modification for specific use cases.
- Main containers include list, vector, stack, queue, and map.
Example: Vector Operations
- Action: Insert an element
-
Method:
v.push_back()(adds to end) - Action: Remove an element
-
Method:
v.pop_back()(removes from end) - Action: Remove all elements
-
Method:
v.clear() - Action: Returns first element
-
Method:
v.begin() - Action: Returns element after last element
-
Method:
v.end() - Action: Returns element at index i
-
Method:
v[i](indexing starts at 0) - Action: Returns vector size
-
Method:
v.size() - Action: Checks if vector is empty
-
Method:
v.empty() - Note: The first element is indexed by 0, the last by size-1.
Container Types
- list: Efficiently inserts and removes elements anywhere, handles memory automatically.
- vector: General-purpose, provides fast access to elements by index, removes elements efficiently from the end but not other positions which have linear time.
- set/map: Access elements by key, fast search capability.
Containers Constructors
-
container<T> c;: Creates an empty container -
container<T> c(c2);: Creates a copy of c2 -
container<T> c(n);: Creates a container with n elements, value-initialized according to type T -
container<T> c(n, t): Creates a container with n elements, initialized to t -
container<T> c(b,e): Creates a container with elements copied from container between b and c.
Container Properties
- Containers have their own elements.
- Elements must support copy/assignment (using an equals
=) - All containers provide
empty()andsize()in constant time. - All containers provide
begin()andend()methods.
C++11 Range-based for Loops
-
for (int i : vec): Simplifies looping through container elements. - Useful if not needing to modify the values in the container.
- If modification is needed the iterator must be modified directly.
Associative Containers
- Used for rapidly retrieving values by key.
- Elements are ordered by key value, supporting fast search.
How Associative Containers Work
- Maps elements based on keys for faster lookups.
- Keys to be comparable to one another.
- Keys are unique, preventing duplicate entries.
- Containers are self-organizing, maintaining order based on keys.
Comparing Key Values
- Uses predefined comparison functions (for built-in types) or user-created ones (for custom types).
- If no built-in comparison exists, the programmer must define a
comparefunction.
Main Operations on Associative Containers
-
begin(): Returns an iterator to the first element. -
end(): Returns an iterator to the element after the last element. -
empty(): Checks if the container is empty. -
size(): Returns the size of the container. -
operator[]: Accesses an element by key. -
insert(): Inserts an element into the container. -
erase(): Removes elements from the container. -
find(): Retrieves an iterator to an element with a specific key. -
lower_bound(): Returns iterator to first element not less than given key. -
upper_bound(): Returns iterator to first element greater than given key.
Using Associative Containers: Example
- Count word occurrences in a sentence using a map.
- Break down a list of names into lists by initial letter.
STL Algorithms
- A set of functions for common tasks on containers.
- They use iterators for access.
- They do not change the containers' structure.
- Not all functions work with all container types.
Function Examples
-
for_each: Applies a function to each element in a range. -
find: Finds a value within a range. -
copy: Copies elements from one range to another. -
replace: Replaces values in a range. -
rotate: Rotates elements within a range. -
set_union: Returns the union of two ordered ranges. -
min_element: Returns the smallest element in a range.
How STL Algorithms Work
- Iterating through containers to access elements.
- Employing function pointers for customization.
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Description
Explore the essential features and functions of STL containers, which help efficiently manage collections of objects in C++. Learn about main container types such as list, vector, stack, queue, and map, and get familiar with common operations on vectors.
