Comment by duped
16 hours ago
That's implementation defined behavior, not undefined behavior. Undefined behavior explicitly refers to something the compiler does not provide a definition for, including "safe defaults."
16 hours ago
That's implementation defined behavior, not undefined behavior. Undefined behavior explicitly refers to something the compiler does not provide a definition for, including "safe defaults."
The C standard says, and I quote:
>Possible undefined behavior ranges from ignoring the situation completely with unpredictable results ... or program execution in a documented manner characteristic of the environment (with or without the issuance of a diagnostic message)
So a compiler is absolutely welcome to make undefined behavior safe. In fact every compiler I know of, such as GCC, clang, MSVC has flags to make various undefined behavior safe, such as signed integer overflow, type punning, casting function pointers to void pointers.
The Linux kernel is notorious for leveraging undefined behavior in C for which GCC guarantees specific and well defined behavior.
It looks like there is also the notion of unspecified behavior, which gives compilers a choice about the behavior and does not require compilers to document that choice or even choose consistently.
And finally there is what you bring up, which is implementation defined behavior which is defined as a subset of unspecified behavior in which compilers must document the choice.
Compilers are not prohibited to provide their own definition for UB, that's how UBsan exists.