Explore the full potential of C++ by mastering the standard library.

Become a C++ Programmer

The C++ standard library is a collection of all the tools and utilities available in C++. It received its latest update in 2017, known as C++17. The update introduces many new features that further optimize our code. This module will help us fully grasp C++ and use it to its full potential.

C++ Standard Library

The default comparison criterion of the ordered associative containers is `std::less`. If we want to use a *user-defined* type as the key, we have to overload the operator `<`. It's sufficient to overload the operator `<` for our data type because the C++ runtime compares, with the help of the relation `(! (elem1<elem2 || elem2<elem1))`, two elements for equality. 

We can specify the sorting criterion as a template argument that must implement a *strict weak ordering*.

><span>ℹ️</span> **Strict weak ordering**
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Strict weak ordering for a sorting criterion on a set `S` is given if the following requirements are met:
> * For every `s` from `S` it has to hold that `s < s` is not possible.
> * For all `s1` and `s2` from `S` it must hold: If `s1 < s2`, then `s2 < s1` is not possible.
> * For all `s1`, `s2` and `s3` with `s1 < s2` and `s2 < s3` the following must hold: `s1 < s3`.
> * For all `s1`, `s2` and `s3` with `s1` not comparable with `s2` and `s2` not comparable with `s3` the following must hold: `s1` is not comparable with `s3`.

In contrast to the definition of the *strict weak ordering*, the usage of a comparison criterion with *strict weak ordering* is a lot simpler for an `std::map`.

This lesson talks about the rules followed by ordered associative containers when comparing the values inside them.

The Comparison Criterion