20 Library introduction [library]

20.5 Library-wide requirements [requirements]

20.5.4 Constraints on programs [constraints]

20.5.4.8 Other functions [res.on.functions]

In certain cases (replacement functions, handler functions, operations on types used to instantiate standard library template components), the C++ standard library depends on components supplied by a C++ program.
If these components do not meet their requirements, this document places no requirements on the implementation.
In particular, the effects are undefined in the following cases: