[std.modules]

# 16 Library introduction [[library]](./#library)

## 16.4 Library-wide requirements [[requirements]](requirements#std.modules)

### 16.4.2 Library contents and organization [[organization]](organization#std.modules)

#### 16.4.2.4 Modules [std.modules]

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lib-intro.tex#L1513)

The C++ standard library provides
the following [*C++ library modules*](#def:C++_library_modules "16.4.2.4 Modules [std.modules]")[.](#1.sentence-1)

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lib-intro.tex#L1517)

The named module std exports declarations in namespace std that are provided by the importable C++ library headers
(Table [24](headers#tab:headers.cpp "Table 24: C++ library headers") or the subset provided by a freestanding implementation)
and the C++ headers for C library facilities (Table [25](headers#tab:headers.cpp.c "Table 25: C++ headers for C library facilities"))[.](#2.sentence-1)

It additionally exports declarations in the global namespace
for the storage allocation and deallocation functions
that are provided by [<new>](support.dynamic.general#header:%3cnew%3e "17.6.1 General [support.dynamic.general]")[.](#2.sentence-2)

[3](#3)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lib-intro.tex#L1526)

The named module std.compat exports the same declarations as
the named module std, and
additionally exports

- [(3.1)](#3.1)

declarations in the global namespace
corresponding to the declarations in namespace std that are provided by
the C++ headers for C library facilities (Table [25](headers#tab:headers.cpp.c "Table 25: C++ headers for C library facilities")),
except the explicitly excluded declarations
described in [[support.c.headers.other]](support.c.headers.other "17.15.7 Other C headers") and

- [(3.2)](#3.2)

declarations provided by
the headers [<stdbit.h>](stdbit.h.syn#header:%3cstdbit.h%3e "22.12 Header <stdbit.h> synopsis [stdbit.h.syn]") and [<stdckdint.h>](stdckdint.h.syn#header:%3cstdckdint.h%3e "29.11.1 Header <stdckdint.h> synopsis [stdckdint.h.syn]")[.](#3.sentence-1)

[4](#4)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lib-intro.tex#L1543)

It is unspecified to which module a declaration in the standard library
is attached[.](#4.sentence-1)

[*Note [1](#note-1)*:

Conforming implementations ensure that mixing#include and import does not result in
conflicting attachments ([[basic.link]](basic.link "6.7 Program and linkage"))[.](#4.sentence-2)

— *end note*]

*Recommended practice*: Implementations should ensure such attachments do not preclude
further evolution or decomposition of the standard library modules[.](#4.sentence-3)

[5](#5)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lib-intro.tex#L1555)

A declaration in the standard library denotes the same entity regardless of
whether it was made reachable through
including a header,
importing a header unit, or
importing a C++ library module[.](#5.sentence-1)

[6](#6)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lib-intro.tex#L1562)

*Recommended practice*: Implementations should avoid exporting any other declarations
from the C++ library modules[.](#6.sentence-1)

[*Note [2](#note-2)*:

Like all named modules, the C++ library modules
do not make macros visible ([[module.import]](module.import "10.3 Import declaration")), such asassert ([[cassert.syn]](cassert.syn "19.3.2 Header <cassert> synopsis")),errno ([[cerrno.syn]](cerrno.syn "19.4.2 Header <cerrno> synopsis")),offsetof ([[cstddef.syn]](cstddef.syn "17.2.1 Header <cstddef> synopsis")), andva_arg ([[cstdarg.syn]](cstdarg.syn "17.14.2 Header <cstdarg> synopsis"))[.](#6.sentence-2)

— *end note*]