16 Library introduction [library]

16.4 Library-wide requirements [requirements]

16.4.2 Library contents and organization [organization]

16.4.2.5 Freestanding implementations [compliance]

Two kinds of implementations are defined: hosted and freestanding ([intro.compliance]); the kind of the implementation is implementation-defined.

For a hosted implementation, this document describes the set of available headers.

A freestanding implementation has an implementation-defined set of headers.

This set shall include at least the headers shown in Table 27 .

Table 27 — C++ headers for freestanding implementations [tab:headers.cpp.fs]

🔗	Subclause	Header
🔗 [support.types]	Common definitions	<cstddef>
🔗 [cstdlib.syn]	C standard library	<cstdlib>
🔗 [support.limits]	Implementation properties	<cfloat>, <climits>, <limits>,
🔗		<version>
🔗 [cstdint.syn]	Integer types	<cstdint>
🔗 [support.dynamic]	Dynamic memory management	<new>
🔗 [support.rtti]	Type identification	<typeinfo>
🔗 [support.srcloc]	Source location	<source_location>
🔗 [support.exception]	Exception handling	<exception>
🔗 [support.initlist]	Initializer lists	<initializer_list>
🔗 [cmp]	Comparisons	<compare>
🔗 [support.coroutine]	Coroutines support	<coroutine>
🔗 [support.runtime]	Other runtime support	<cstdarg>
🔗 [concepts]	Concepts library	<concepts>
🔗 [errno]	Error numbers	<cerrno>
🔗 [syserr]	System error support	<system_error>
🔗 [debugging]	Debugging	<debugging>
🔗 [memory]	Memory	<memory>
🔗 [type.traits]	Type traits	<type_traits>
🔗 [ratio]	Compile-time rational arithmetic	<ratio>
🔗 [utility]	Utility components	<utility>
🔗 [tuple]	Tuples	<tuple>
🔗 [optional]	Optional objects	<optional>
🔗 [variant]	Variants	<variant>
🔗 [expected]	Expected objects	<expected>
🔗 [function.objects]	Function objects	<functional>
🔗 [bit]	Bit manipulation	<bit>
🔗 [array]	Class template array	<array>
🔗 [inplace.vector]	Class template inplace_vector	<inplace_vector>
🔗 [views.contiguous]	Contiguous access	<span>
🔗 [views.multidim]	Multidimensional access	<mdspan>
🔗 [iterators]	Iterators library	<iterator>
🔗 [ranges]	Ranges library	<ranges>
🔗 [algorithms]	Algorithms library	<algorithm>, <numeric>
🔗 [string.view]	String view classes	<string_view>
🔗 [string.classes]	String classes	<string>
🔗 [c.strings]	Null-terminated sequence utilities	<cstring>, <cwchar>
🔗 [charconv]	Primitive numeric conversions	<charconv>
🔗 [c.math]	Mathematical functions for floating-point types	<cmath>
🔗 [atomics]	Atomics	<atomic>
🔗

For each of the headers listed in Table 27, a freestanding implementation provides at least the freestanding items ([freestanding.item]) declared in the header.

The hosted library facilities are the set of facilities described in this document that are required for hosted implementations, but not required for freestanding implementations.

A freestanding implementation provides a (possibly empty) implementation-defined subset of the hosted library facilities.

Unless otherwise specified, the requirements on each declaration, entity, typedef-name, and macro provided in this way are the same as the corresponding requirements for a hosted implementation, except that not all of the members of the namespaces are required to be present.

A freestanding implementation provides deleted definitions ([dcl.fct.def.delete]) for a (possibly empty) implementation-defined subset of the namespace-scope functions and function templates from the hosted library facilities.

[Note 1:

An implementation can provide a deleted definition so that the result of overload resolution does not silently change when migrating a program from a freestanding implementation to a hosted implementation.

— end note]