16 Library introduction [library]

16.4 Library-wide requirements [requirements]

16.4.5 Constraints on programs [constraints]

16.4.5.3 Reserved names [reserved.names]

16.4.5.3.5 Types [extern.types]

For each type T from the C standard library, the types ​::​T and std​::​T are reserved to the implementation and, when defined, ​::​T shall be identical to std​::​T.