C++26 Contracts: Introduction to Preconditions and Postconditions
This technical article explains the implementation of 'contracts' in C++26, specifically focusing on preconditions and postconditions. It demonstrates how to use new syntax to enforce code requirements directly within function declarations.
Why it matters
Improved contract support in C++ helps developers write safer, more robust code by explicitly defining expected behavior at the language level.
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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