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]

1
#
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.
2
#
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
Common definitions
<cstddef>
C standard library
<cstdlib>
Implementation properties
<cfloat>, <climits>, <limits>,
<version>
Integer types
<cstdint>
Dynamic memory management
<new>
Type identification
<typeinfo>
Source location
<source_location>
Exception handling
<exception>
Initializer lists
<initializer_list>
Comparisons
<compare>
Coroutines support
<coroutine>
Other runtime support
<cstdarg>
Concepts library
<concepts>
Error numbers
<cerrno>
System error support
<system_error>
Debugging
<debugging>
Memory
<memory>
Type traits
<type_traits>
Compile-time rational arithmetic
<ratio>
Utility components
<utility>
Tuples
<tuple>
Optional objects
<optional>
Variants
<variant>
Expected objects
<expected>
Function objects
<functional>
Bit manipulation
<bit>
Class template array
<array>
Class template inplace_vector
<inplace_vector>
Contiguous access
<span>
Multidimensional access
<mdspan>
Iterators library
<iterator>
Ranges library
<ranges>
Algorithms library
<algorithm>, <numeric>
String view classes
<string_view>
String classes
<string>
Null-terminated sequence utilities
<cstring>, <cwchar>
Primitive numeric conversions
<charconv>
Mathematical functions for floating-point types
<cmath>
Atomics
<atomic>
3
#
For each of the headers listed in Table 27, a freestanding implementation provides at least the freestanding items ([freestanding.item]) declared in the header.
4
#
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.
5
#
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]