C++20 was supposed to have them, but they were removed on the very last minute, if we are lucky maybe C++23 will get them, but C++26 is most likely, if they ever go forward with them. [1]

For C you can have a look at Frama-C. [2]

D also has DbC. [3]

In case you can target Windows only, VC++ supports SAL Annotations, while not DbC they help to improve code security

[1] - http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p233...

[2] - https://frama-c.com/html/acsl.html

[3] - https://dlang.org/spec/contracts.html

[4] - https://docs.microsoft.com/en-us/cpp/code-quality/using-sal-...