How to add elements to C++ STL container?

There are 2 ways to add elements to an STL container: the container uses push_back and emplace_back to add elements, and the associated container uses insert and emplace key-value pairs to insert elements.

#How to add elements to a C++ STL container?

The C++ Standard Template Library (STL) provides powerful container classes for storing and managing data. Adding elements to these containers can be done in a variety of ways. This article will introduce different ways to add elements using STL containers and provide practical examples.

Container Types

STL provides a variety of container types, including the following:

• Containers: For example vector and list, which store elements in order.
• Associative containers: Such as map and set, which allow elements to be found based on key values.

Methods to add elements

Container

Methods to add elements to a container include:

• push_back: Adds elements to the end of the container.
• emplace_back: Create a new element in the container to avoid unnecessary copying.
• insert: Insert an element at a specific position.

Associated container

Methods to add elements to the associated container include:

• insert: will Key-value pairs are inserted into the container.
• emplace: Creates a new element and inserts it into the container.

Practical case

Add elements to vector:

#include <vector>

int main() {
  // 创建一个 vector
  std::vector<int> numbers;

  // 使用 push_back 添加元素
  numbers.push_back(1);
  numbers.push_back(3);
  numbers.push_back(5);

  // 使用 emplace_back 添加元素
  numbers.emplace_back(7);

  // 打印 vector
  for (auto& number : numbers) {
    std::cout << number << " ";
  }

  return 0;
}

Add elements to map ：

#include <map>

int main() {
  // 创建一个 map
  std::map<std::string, int> ages;

  // 使用 insert 添加元素
  ages["John"] = 25;
  ages["Mary"] = 30;

  // 使用 emplace 添加元素
  ages.emplace("Bob", 35);

  // 打印 map
  for (auto& [name, age] : ages) {
    std::cout << name << ": " << age << std::endl;
  }

  return 0;
}

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