● Covered by 1 source · 1 reportMedium impact1 neutral
C++26 Introduces Standard Library Hardening for Improved Safety
Key points
- C++26 introduces Standard Library hardening.
- Hardening converts undefined behavior into contract violations with terminating semantics.
- This applies to operations like `std::vector::operator[]` for out-of-bounds access.
- The feature is linked to the new Contracts model in C++26.
Understanding Standard Library Hardening
The C++26 standard introduces the concept of a "hardened" implementation for its Standard Library. This mode is designed to improve program safety by providing defined behavior in situations that would otherwise result in undefined behavior, such as accessing elements outside the bounds of a `std::vector` using `operator[]`.
How Hardening Works
In a hardened Standard Library implementation, an operation that violates a precondition (e.g., out-of-bounds access) will trigger a contract violation with a terminating semantic. This means the program will stop execution rather than continuing with potentially memory-unsafe undefined behavior. The specific method for enabling this hardened mode is implementation-defined.
Distinction from `at()` and Contracts Integration
Hardening `operator[]` does not convert it into `at()`, which throws `std::out_of_range` exceptions. Instead, it detects programming errors and terminates the program, offering a different error-handling approach. This feature is closely tied to the new Contracts model accepted into C++26, where hardened preconditions must use a terminating semantic, unlike ordinary contracts which can have various semantics like ignore, observe, enforce, or quick-enforce.
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Primary sources
GitHub microsoft/STLReporting from
C++26 will include a new "hardened" mode for its Standard Library, which aims to prevent undefined behavior by terminating execution upon detection of programming errors. This feature, tied to the new Contracts model, provides a defined error handling mechanism for operations like `std::vector::operator[]` where out-of-bounds access would typically lead to undefined behavior.