[basic.contract.handler]

The contract-violation handler of a program is a function named ::handle_contract_violation.

The contract-violation handler shall have a single parameter of type “lvalue reference to const std::contracts::contract_violation” and shall return void.

The contract-violation handler may have a non-throwing exception specification.

The implementation shall provide a definition of the contract-violation handler, called the default contract-violation handler.

[Note 1:

No declaration for the default contract-violation handler is provided by any standard library header.

— end note]

Recommended practice: The default contract-violation handler should produce diagnostic output that suitably formats the most relevant contents of the std::contracts::contract_violation object, rate-limited for potentially repeated violations of observed contract assertions, and then return normally.

It is implementation-defined whether the contract-violation handler is replaceable ([dcl.fct.def.replace]).

If the contract-violation handler is not replaceable, a declaration of a replacement function for the contract-violation handler is ill-formed, no diagnostic required.