Introduction to STL Containers

Introduction to STL Containers

• STL containers are used to solve complex problems.
• They provide useful functions and data structures.
• They ensure consistency between containers.
• Containers are collections of objects defined using template classes.
• Templates keep the container separate from the data type.
• Container types are optimized for specific uses (e.g., access and modification).
• Common containers include lists, vectors, stacks, queues, and maps.

Example: Vector Operations

• Action: Insert an element
• Method: v.push_back()
• Action: Remove an element
• Method: v.pop_back()
• Action: Remove all elements
• Method: v.clear()
• Action: Return first element
• Method: v.begin()
• Action: Return one past the last element
• Method: v.end()
• Action: Return the ith element
• Method: v[i]
• Action: Get the vector size
• Method: v.size()
• Action: Check for emptiness
• Method: v.empty()
• Note: Vector indexing starts from 0, and the last element is size-1.

Container Types

• list:
  • Inserts and removes elements anywhere in constant time.
  • Uses automatic memory management.
• vector:
  • General-purpose container.
  • Provides fast access by index (constant time).
  • Removes elements from the end in constant time; other inserts/removals are linear.
• set/map:
  • Access element by key in constant time.
  • Enables fast searching.

Containers Constructors

• #include <list>
• #include <vector>
• Example list<int> oneList; creates an empty list of integers.
• Example list<double> secondList(10, 4.22); creates a list with 10 doubles all set to 4.22.
• Example list<double> thirdList(secondList); creates a copy of secondList.
• Different constructor options create empty, copy or initialized lists.

Container Properties

• Containers have their own elements.
• Elements need to support copy and assignment.
• All containers have empty() and size() methods in constant time.
• All containers have begin() and end() methods.

Choosing the Right Container

• Purpose: How elements will be accessed (randomly, sequentially).
• Modifications: Additions, removals, and sorting.
• Performance: Access and modification times depend on the number of elements (linear, log, or exponential time complexity).
• Memory usage.

Iterators

• Iterators: generalized pointers for accessing elements sequentially.
• Optimizations related to container type.
• Definition: Identifiers for container and element. Enables examining stored values and moving among elements.
• Restrictions on operations to ensure efficiency with different container types.

Using Iterators

• Example using iterators to access vector elements.
• Using begin() and end() methods.

Associative Containers

• Goal: Efficiently find elements.
• Sequential search is slow.
• Associative containers arrange elements based on value.
• Enables fast search through order or structure.
• Contains more information (like key).

Map Example

• Key-value pairs.
• Keys associated with values until deletion.
• Keys are not restricted to integers (any comparable type is valid).
• Unique keys.
• Self-ordering containers (program cannot change element order).

Using Associative Containers

• Class pair: simple data structure with first and second elements.
• Map elements are pairs (first: key, second: associated value).
• Iterators are used to access keys and values.
• Use structure to count occurrences in a sentence or group names by first letter.

Comparing Functions

• Use defined comparison functions for built-in types and types with comparison functions.
• When no comparison function exists, the programmer must provide one.
• map constructors that take a comparison function as a parameter (for specialized orderings).

Main Operations on Associative Containers

• Declaration
• begin(): Return iterator to beginning
• end(): Return iterator to end
• empty(): Test whether container is empty
• size(): Return container size
• operator[]: Access element
• insert(pair); Insert element
• erase(): Erase elements
• find(): Returns iterator to an element
• lower_bound(): Iter to lower bound of element(s)
• upper_bound(): Iter to upper bound of element(s)

Using Associative Containers, Example

• Example using a map to store words and their counts.
• Example of using a map to group names based on their first letter.

Standard Library Algorithms

• STL Algorithm: Set of functions tailored for use with containers.
• Iterators/pointers essential for element access within containers.
• STL Algorithm operations do not modify container structure.
• Not all functions work with every container type.

Functions Example

• for_each(): Applies a function to a range of elements.
• find(): Searches for a specific value in a range.
• copy(): Copies a range of elements.
• replace(): Replaces values in a range.
• rotate(): Rotates elements in a range.
• set_union(): Returns the union of two sorted ranges.
• min_elements(): Returns the smallest element in a range.

How Algorithms Work

• Iterators enable algorithm access to container elements.
• Template functions allow using algorithms with different container types.
• Example of the function for_each() applied to containers.

This quiz covers the basics of Standard Template Library (STL) containers in C++. You'll learn about different types of containers, their functions, and methods for manipulating data within these containers, such as vectors, lists, and maps. Test your knowledge on how these containers optimize data handling in C++ programming.