16 Library introduction [library]

16.4 Library-wide requirements [requirements]

16.4.2 Library contents and organization [organization] Library contents [contents]

The C++ standard library provides definitions for the entities and macros described in the synopses of the C++ standard library headers ([headers]), unless otherwise specified.
All library entities except operator new and operator delete are defined within the namespace std or namespaces nested within namespace std.147
It is unspecified whether names declared in a specific namespace are declared directly in that namespace or in an inline namespace inside that namespace.148
Whenever an unqualified name other than swap, make_error_code, make_error_condition, or submdspan_mapping is used in the specification of a declaration D in [support] through [thread] or [depr], its meaning is established as-if by performing unqualified name lookup ([basic.lookup.unqual]) in the context of D.
[Note 1: 
Argument-dependent lookup is not performed.
— end note]
Similarly, the meaning of a qualified-id is established as-if by performing qualified name lookup ([basic.lookup.qual]) in the context of D.
[Example 1: 
The reference to is_array_v in the specification of std​::​to_array ([array.creation]) refers to ​::​std​::​is_array_v.
— end example]
[Note 2: 
Operators in expressions ([over.match.oper]) are not so constrained; see [global.functions].
— end note]
The meaning of the unqualified name swap is established in an overload resolution context for swappable values ([swappable.requirements]).
The meanings of the unqualified names make_error_code, make_error_condition, and submdspan_mapping are established as-if by performing argument-dependent lookup ([basic.lookup.argdep]).
The C standard library headers ([support.c.headers]) also define names within the global namespace, while the C++ headers for C library facilities ([headers]) can also define names within the global namespace.
This gives implementers freedom to use inline namespaces to support multiple configurations of the library.