In many cases, what is considered UB in the C standard is a widely accepted and documented extension in the vast majority of compilers. For example, nonstrict a

In many cases, what is considered UB in the C standard is a widely accepted and documented extension in the vast majority of compilers. For example, nonstrict aliases are UB in ISO C, but are defined language extensions in MSVC, GCC, clang, and many other compiler vendors.