C++ std::map Usage Explained

std::map is an associative container in the C++ standard library used to store key-value pairs. It internally utilizes a Red-Black Tree to ensure the ordering of the key-value pairs.

You can quickly find the corresponding value based on the key using std::map, with a time complexity of O(log n). You can insert, delete, and search for elements using std::map member functions, and it also supports traversal operations.

Here are some common methods for std::map:

1. insert a key-value pair into the map: this function allows you to add a key and its corresponding value into the map.
2. Delete the key in the map corresponding to the specified key.
3. Search for the value corresponding to the specified key in the map.
4. begin() and end(): return iterators pointing to the first and last element of the map, used to iterate through the elements in the map.
5. size(): Returns the number of elements in the map.
6. empty(): determine if the map is empty.

Example code:

#include <iostream>
#include <map>

int main() {
    std::map<int, std::string> myMap;

    myMap.insert(std::make_pair(1, "apple"));
    myMap.insert(std::make_pair(2, "banana"));
    myMap.insert(std::make_pair(3, "cherry"));

    std::map<int, std::string>::iterator it;
    for (it = myMap.begin(); it != myMap.end(); ++it) {
        std::cout << it->first << " => " << it->second << std::endl;
    }

    if (myMap.find(2) != myMap.end()) {
        std::cout << "Found key 2 with value: " << myMap[2] << std::endl;
    }

    myMap.erase(3);

    std::cout << "Map size: " << myMap.size() << std::endl;

    return 0;
}

The code above demonstrates how to insert, search, and remove elements using std::map, as well as how to iterate through all elements in the map.