Using std::map with a custom class key


This problem in an OOP paradigm is that it will be viewed in terms of the objects involved, which are cars, trucks, buses, scooters, taxis, and people crossing by. These objects will have some characteristics as well. Like a four-wheeler vehicle will have a steering wheel, motor brakes, and so on. And its behavior will be its mobility. So, here, a car will be an object for a class named Vehicle. Clang is still adding support for Class Template Argument Deduction as much of the standard library had to be rewritten to accommodate the feature.

Before we move on to what iterators are there in the map class let us have a recap of what iterators are in C++. Functions, that perform different map operations. We shall look into them one by one and try to understand how they work through examples.

In this lesson, we’ll use programming to try to solve the Map In C++ Sorted Descending Order puzzle. The code shown below demonstrates this. Please use our online compiler to post code in comments using C, C++, Java, Python, JavaScript, C#, PHP, and many more popular programming languages.

This function returns a pointer pointing corresponding to the key or will point before the key value. This function returns a pointer pointing corresponding to the key or will point after the key value. This function returns a key and the element corresponding to it. Empty() function is a member function of C++ Map with boolean datatype. It checks if the container is empty or not.

This pointer can point in either direction of the container and hence it is bidirectional. In above example we sorted the contents of a map in ascending order of value. If you want to sort the map contents in descending order then use following lambda function in above example i.e. Then we will copy the elements from map to set and it will store them in sorted order of values. Unsorted by string literals, but sorted by pointers.

HashMap allows a single null key and multiple null values. TreeMap does not allow null keys but can have multiple null values. HashMap allows heterogeneous elements because it does not perform sorting on keys. TreeMap allows homogeneous values as a key because of sorting. To reverse sort map entries, pass Collections.

A key of 5 and a value of 6 will be inserted into the map. Create a map named m where the keys will be integers, and the values will be integers. Three entries have been made into the map.

While the value elements will be another map that can store integer key-value pairs. You can modify the map according to your program needs and even have a vector or map inside a map. Maps are associative containers that store elements formed by a combination of a key value and a mapped value, following a specific order.

These member functions are predefined, and you do not have to define them again in your code. C++ Map also contains various swimming lesson plans pdf member functions that will be discussed in this section. The lambda expression for our problem can be seen below.