97 lines
4.8 KiB
Markdown
97 lines
4.8 KiB
Markdown
[using]
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# 16 Library introduction [[library]](./#library)
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## 16.4 Library-wide requirements [[requirements]](requirements#using)
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### 16.4.3 Using the library [using]
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#### [16.4.3.1](#overview) Overview [[using.overview]](using.overview)
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[1](#overview-1)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lib-intro.tex#L1678)
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Subclause [using] describes how a C++ program gains access to the facilities of the
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C++ standard library[.](#overview-1.sentence-1)
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[[using.headers]](#headers "16.4.3.2 Headers") describes effects during translation
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phase 4, while [[using.linkage]](#linkage "16.4.3.3 Linkage") describes effects during [phase
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8](lex.phases "5.2 Phases of translation [lex.phases]")[.](#overview-1.sentence-2)
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#### [16.4.3.2](#headers) Headers [[using.headers]](using.headers)
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[1](#headers-1)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lib-intro.tex#L1686)
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The entities in the C++ standard library are defined in headers,
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whose contents are made available to a translation unit when it contains the appropriate#include preprocessing directive ([[cpp.include]](cpp.include "15.3 Source file inclusion"))
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or the appropriateimport declaration ([[module.import]](module.import "10.3 Import declaration"))[.](#headers-1.sentence-1)
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[2](#headers-2)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lib-intro.tex#L1698)
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A translation unit may include library headers in any order ([[lex.separate]](lex.separate "5.1 Separate translation"))[.](#headers-2.sentence-1)
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Each may be included more than once, with no effect different from
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being included exactly once, except that the effect of including either[<cassert>](assertions.general#header:%3ccassert%3e "19.3.1 General [assertions.general]") or [<assert.h>](support.c.headers.general#header:%3cassert.h%3e "17.15.1 General [support.c.headers.general]") depends each time on the lexically current definition ofNDEBUG[.](#headers-2.sentence-2)[149](#footnote-149 "This is the same as the C standard library.")
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[3](#headers-3)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lib-intro.tex#L1712)
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A translation unit shall include a header only outside of anydeclaration or definition and,
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in the case of a module unit,
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only in its [*global-module-fragment*](module.global.frag#nt:global-module-fragment "10.4 Global module fragment [module.global.frag]"), and
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shall include the header or import the corresponding header unit lexically
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before the first reference in that translation unit to any of the entities
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declared in that header[.](#headers-3.sentence-1)
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No diagnostic is required[.](#headers-3.sentence-2)
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[149)](#footnote-149)[149)](#footnoteref-149)
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This is the same as the C standard library[.](#footnote-149.sentence-1)
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#### [16.4.3.3](#linkage) Linkage [[using.linkage]](using.linkage)
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[1](#linkage-1)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lib-intro.tex#L1724)
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Entities in the C++ standard library have [external linkage](basic.link "6.7 Program and linkage [basic.link]")[.](#linkage-1.sentence-1)
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Unless otherwise specified, objects and functions have the defaultextern "C++" linkage ([[dcl.link]](dcl.link "9.12 Linkage specifications"))[.](#linkage-1.sentence-2)
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[2](#linkage-2)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lib-intro.tex#L1730)
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Whether a name from the C standard library declared with
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external linkage hasextern "C" orextern "C++" linkage is implementation-defined[.](#linkage-2.sentence-1)
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It is recommended that an
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implementation useextern "C++" linkage for this purpose[.](#linkage-2.sentence-2)[150](#footnote-150 "The only reliable way to declare an object or function signature from the C standard library is by including the header that declares it, notwithstanding the latitude granted in ISO/IEC 9899:2024, 7.1.4.")
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[3](#linkage-3)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lib-intro.tex#L1751)
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Objects and functions
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defined in the library and required by a C++ program are included in
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the program prior to program startup[.](#linkage-3.sentence-1)
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[4](#linkage-4)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/lib-intro.tex#L1757)
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See also[replacement functions](replacement.functions "16.4.5.6 Replacement functions [replacement.functions]"),[runtime changes](handler.functions "16.4.5.7 Handler functions [handler.functions]")[.](#linkage-4.sentence-1)
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[150)](#footnote-150)[150)](#footnoteref-150)
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The only reliable way to declare an object or
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function signature from the C standard library is by including the header that
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declares it, notwithstanding the latitude granted in ISO/IEC 9899:2024, 7.1.4[.](#footnote-150.sentence-1)
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