C++ STL Tutorial

The C++ Standard Template Library (STL) is a powerful collection of C++ template classes and functions that provides a series of generic, reusable algorithms and data structures.

STL's design is based on generic programming, which means that templates can be used to write code independent of any specific data type.

STL is divided into multiple components, including Containers, Iterators, Algorithms, Function Objects, and Adapters, etc.

Benefits of using STL:

Code Reuse: STL provides a large number of generic data structures and algorithms, reducing the work of writing repetitive code.
Performance Optimization: The algorithms and data structures in STL are optimized to provide the best performance.
Generic Programming: Using templates, STL supports generic programming, allowing algorithms and data structures to apply to any data type.
Easy to maintain: STL's design makes code more modular and easier to read and maintain.

The core of the C++ Standard Template Library includes the following important components:

Components	Description
Containers	Containers are one of the most basic components in STL. They provide various data structures, including vector, list, queue, stack, set, map, and so on. These containers have different characteristics and uses, so you can choose the appropriate container based on actual needs.
Algorithms	STL provides a large number of algorithms for performing various operations on elements in containers, including sorting, searching, copying, moving, transforming, etc. When using these algorithms, there is no need to care about the specific type of container; you only need to specify the range to be operated on.
Iterators	Iterators are used to traverse the elements in containers, allowing elements to be accessed in a unified way without worrying about the internal implementation details of the container. STL provides many types of iterators, including random access iterators, bidirectional iterators, forward iterators, and input/output iterators, among others.
Function Objects	Function objects are objects that can be called like functions and can be used for various operations in algorithms. STL provides a variety of function objects, including unary function objects, binary function objects, predicates, and more, to meet different needs.
Adapters	Adapters are used to adapt one container or iterator into another container or iterator to meet specific requirements. STL provides a variety of adapters, including stack adapter, queue adapter, and priority queue adapter, among others.

These components all come with a rich set of predefined functions, helping us handle complex tasks in a simple way.

Container

Containers are sequences used to store data, and they provide different storage methods and access modes.

Containers in STL can be divided into three categories:

1. Sequence containers: store sequences of elements and allow bidirectional traversal.

std::vector: dynamic array, supports fast random access.
std::deque: double-ended queue, supports fast insertion and deletion.
std::list: linked list, supports fast insertion and deletion, but does not support random access.

2. Associative containers: store key-value pairs. Each element has a key and a value, and elements are organized by keys.

std::set: set, duplicate elements are not allowed.
std::multiset: multiset, allows multiple elements to have the same key.
std::map: map, each key maps to a value.
std::multimap: multimap, stores key-value pairs (pair), where keys are not unique and values can be repeated, allowing one key to map to multiple values.

3. Unordered containers (introduced in C++11): hash tables, support fast lookup, insertion, and deletion.

std::unordered_set: unordered set.
std::unordered_multiset: unordered multiset.
std::unordered_map: unordered map.
std::unordered_multimap: unordered multimap.

The following program demonstrates the vector container (a C++ standard template), which is very similar to an array. The only difference is that when the vector needs to expand its size, it automatically handles its own storage requirements:

Example

#include <iostream> #include <vector> using namespace std; int main() { // Create a vector to store int vector<int> vec; int i; // Display the original size of vec cout << "vector size = " << vec.size() << endl; // Push 5 values into the vector for(i = 0; i < 5; i++){ vec.push_back(i); } // Display the size of vec after expansion cout << "extended vector size = " << vec.size() << endl; // Access the 5 values in the vector for(i = 0; i < 5; i++){ cout << "value of vec [" << i << "] = " << vec[i] << endl; } // Use iterator to access the values vector<int>::iterator v = vec.begin(); while( v != vec.end()) { cout << "value of v = " << *v << endl; v++; } return 0; }

When the above code is compiled and executed, it produces the following results:

vector size = 0
extended vector size = 5
value of vec [0] = 0
value of vec [1] = 1
value of vec [2] = 2
value of vec [3] = 3
value of vec [4] = 4
value of v = 0
value of v = 1
value of v = 2
value of v = 3
value of v = 4

Regarding the various functions used in the above example, there are a few points to note:

The push_back( ) member function inserts a value at the end of the vector, expanding the vector's size if necessary.
The size( ) function displays the size of the vector.
The begin( ) function returns an iterator pointing to the beginning of the vector.
The end( ) function returns an iterator pointing to the end of the vector.

STL is an indispensable part of C++ programming. It greatly expands the functionality of C++, allowing programmers to write more efficient and more readable code.

Mastering the use of STL is very important for any C++ programmer.

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