C++26 Contracts: Introduction to Preconditions and Postconditions

This article explores the concept of contracts in C++26, focusing on how to express preconditions and postconditions in code. It discusses the transition from assertions to contract-based programming, providing examples and insights into the new syntax.

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In the article about Standard Library hardening , we looked at checks for invalid Standard Library container access and other broken preconditions. I mentioned that those requirements are expressed in terms of “contracts”. But what about our code?

In this post, we’ll explore contracts from C++26. We’ll start with a simple cassert , move the requirement into the function itself, and see how to check results. We’ll also look at declarations and definitions, compiler options, and a few details that can surprise you.

// foo.h #include <vector> int get_value ( const std :: vector < int >& values , std :: size_t index ); And the implementation:

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