Master the efficient use of C + + containers and STL

In C + + programming, containers and STL (Standard Template Library) are two crucial concepts.

They provide developers with powerful tools for storing and managing data while improving code efficiency and readability.

This article will delve into the relationship between C + + containers and STL, and provide some efficient usage skills to improve your code performance and take your C + + projects to the next level.

1. The relationship between C + + containers and STL.

STL is part of the C + + standard library, which provides a common set of efficient containers and algorithms.

These containers and algorithms allow developers to easily handle various data structures without having to implement complex data management logic from scratch.

Common STL containers include vector、list、deque、set、mapWait.

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1.1 Container classification.

STL containers can be divided into two categories: serial containers and relational containers: - # Sequential Container #: The elements are arranged in linear order, such as vector、deque、listWait.

- # Associative Container #: The elements are arranged in a specific order, such as set、mapWait.

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1.2 Container characteristics.

Each container has its own specific characteristics and applicable scenarios: \n-vector: Dynamic array, supports fast random access, but is inefficient when inserting or deleting elements in the middle.

\n-list: Doubly linked list, suitable for frequent insertion and deletion operations, but does not support fast random access.

\n-deque: Double-ended queue, combined with vectorSumlistThe advantages of supporting fast insertion and deletion at both ends.

\n-set: Ordered collection, repeating elements are not allowed, and the interior is usually implemented as a red-black tree.

\n-map: key-value pair collection, key sorting, the internal implementation is usually a balanced binary search tree.

2. Master the efficient use of C + + containers and STL.

To take full advantage of STL containers and algorithms and improve code performance, here are some practical tips and best practices: \n#

2.1 Choose the right container.

Choose the appropriate container type according to your specific needs.

For example, if frequent random access is required, you can choose vector; If frequent insert and delete operations are required, you can choose listOrdeque。

#include 
#include 
#include 
#include 

int main() {
    std::vector v = {1, 2, 3, 4, 5}; // 适用于随机访问
    std::list l = {1, 2, 3, 4, 5};   // 适用于频繁插入和删除
    std::deque d = {1, 2, 3, 4, 5};  // 适用于两端操作
}

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2.2 Avoid unnecessary copying.

Try to use references or pointers to pass container objects to avoid unnecessary copy operations.

void process(const std::vector& vec) {
    for (const auto& val : vec) {
        std::cout << val << " ";
    }
}

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2.3 Pre-allocated memory.

For vectorSuch as dynamic arrays, pre-allocating enough memory can reduce the number of memory reallocations, thereby improving performance.

std::vector vec;
vec.reserve(100); // 预分配100个元素的空间
for (int i = 0; i < 100; ++i) {
    vec.push_back(i);
}

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2.4 Use iterators instead of indexes.

For serial containers, traversing using iterators instead of indexes can improve code readability and security.

std::vector vec = {1, 2, 3, 4, 5};
for (auto it = vec.begin(); it != vec.end(); ++it) {
    std::cout << *it << " ";
}

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2.5 Utilize the algorithm library.

STL provides a rich algorithm library, such as sort、find、copyEtc., which can simplify the code and increase efficiency.

#include 
#include 
#include 

int main() {
    std::vector vec = {5, 3, 1, 4, 2};
    std::sort(vec.begin(), vec.end()); // 使用STL算法进行排序
    for (const auto& val : vec) {
        std::cout << val << " ";
    }
}

3. Best practices to improve code performance.

In addition to the above tips, there are some best practices that can help you further improve code performance: \n#

3.1 Avoid unnecessary temporary objects.

Minimize the creation of temporary objects, and move semantics can be used to optimize performance.

std::vector createVector() {
    return std::vector{1, 2, 3, 4, 5}; // 返回一个临时对象
}

int main() {
    std::vector vec = createVector(); // 可能触发拷贝构造函数
}

After improvement:

std::vector createVector() {
    return std::vector{1, 2, 3, 4, 5}; // 返回一个临时对象
}

int main() {
    std::vector vec = std::move(createVector()); // 使用移动语义避免拷贝
}

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3.2 Use smart pointers to manage resources.

For dynamically allocated resources, use smart pointers (such as std::unique_ptrSumstd::shared_ptr) can automatically manage memory, reducing the risk of memory leaks.

#include 
#include 

class MyClass {
public:
    void display() const { std::cout << "Hello, World!" << std::endl; }
};

int main() {
    std::unique_ptr ptr = std::make_unique(); // 使用智能指针管理资源
    ptr->display();
}

4. Summary.

By understanding the relationship between C + + containers and STL, and mastering efficient usage skills and best practices, you can significantly improve the performance and maintainability of your code.

Choosing the right container type, avoiding unnecessary copying, pre-allocating memory, using iterators and algorithm libraries, and adopting modern C + + features such as moving semantics and smart pointers are all effective ways to improve code performance.

I hope the content of this article can help you achieve better results in C + + projects.