C STL is a set of general template classes and functions, including core components such as containers, algorithms, and iterators. Containers such as vector, list, map, and set are used to store data. Vector supports random access and is suitable for frequent reading; list insertion and deletion are efficient but access is slow; map and set are based on red and black trees, and automatic sorting is suitable for fast searches. Algorithms such as sort, find, copy, transform, and accumulate are commonly used to encapsulate them, and act on the iterator range of the container. The iterator acts as a bridge connecting containers to algorithms, supporting traversal and accessing elements. Other components include function objects, adapters, allocators, which are used to customize logic, change behavior, and memory management. STL simplifies C programming, improving efficiency and code reuse.

C's Standard Template Library (STL) is a common set of template classes and functions used to implement common data structures and algorithms. It is not an integral part of the C language itself, but it is widely integrated into the standard library and has become an important tool for modern C programming.

Container: "box" that stores data

The most core part of STL is containers, which are used to organize and store different types of data. Commonly used containers include vector , list , map , set , etc.

• vector is similar to dynamic arrays, supports random access, and is suitable for frequent read scenarios.
• list is a two-way linked list, with high insertion and deletion efficiency, but slow access to elements.
• map and set are based on red and black trees and are automatically sorted, suitable for occasions where quick searches and unique key values ??are needed.

For example: If you are dealing with a set of changing student scores, using vector may be more convenient than fixed-length arrays:

 std::vector<int> scores = {85, 90, 78};
scores.push_back(93); // Add new score

Different containers have different scenarios. When choosing, you should consider the access frequency and the cost of insertion and deletion operations.

Algorithm: Commonly used package

STL provides a rich set of algorithms (Algorithms), such as sorting, searching, copying, transformation, etc. These algorithms usually act on the iterator range of the container.

For example, sorting vectors using std::sort is very simple:

 std::sort(scores.begin(), scores.end());

Common algorithms include:

• find : Find whether an element exists
• copy : Copy the contents of one container to another
• transform : performs some kind of transformation operation on each element
• accumulate : sum or custom accumulation operations

The benefit of these algorithms is that they have been optimized and can be used with any compatible container, reducing the work of re-making wheels.

Iterator: a bridge connecting containers and algorithms

Iterators are objects used in STL to traverse container elements, a bit like pointers. It allows the algorithm to not know the internal structure of the specific container, but only needs to access the elements through an iterator.

You can think of an iterator as a "page turner" and view data page by page. for example:

 for (auto it = scores.begin(); it != scores.end(); it) {
    std::cout << *it << " ";
}

STL supports multiple types of iterators, such as forward, reverse, constant iterators, etc. Understanding their differences can help write more efficient and secure code.

Other components: adapters, functors, allocators, etc.

In addition to the above three core parts, STL also includes some auxiliary components:

• Function Objects (Functors) : Objects that can be called like functions, often used to customize sorting or operation logic.
• Adaptors : Change the behavior of existing components, such as stack or queue , is a deque -based adapter.
• Allocators : Responsible for memory management, and by default, it rarely needs to be implemented by itself.

Although these components are not as frequently used in daily development as containers and algorithms, they come in handy in advanced applications or performance optimization.

In general, STL provides efficient, flexible, and reusable data structures and algorithms, greatly simplifying C development work. Mastering its basic usage is a key step to becoming a qualified C programmer. Basically that's it.

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