[diff.cpp17.library]

# Annex C (informative) Compatibility [[diff]](./#diff)

## C.3 C++ and ISO C++ 2017 [[diff.cpp17]](diff.cpp17#library)

### C.3.10 [[library]](library "16 Library introduction"): library introduction [diff.cpp17.library]

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/compatibility.tex#L1329)

**Affected subclause:** [[headers]](headers)  


**Change:** New headers[.](#1.sentence-1)

  


**Rationale:** New functionality[.](#1.sentence-2)

  


**Effect on original feature:** The following C++ headers are new:[<barrier>](barrier.syn#header:%3cbarrier%3e "32.9.3.2 Header <barrier> synopsis [barrier.syn]"),[<bit>](bit.general#header:%3cbit%3e "22.11.1 General [bit.general]"),[<charconv>](charconv.syn#header:%3ccharconv%3e "28.2.1 Header <charconv> synopsis [charconv.syn]"),[<compare>](compare.syn#header:%3ccompare%3e "17.12.1 Header <compare> synopsis [compare.syn]"),[<concepts>](concepts.syn#header:%3cconcepts%3e "18.3 Header <concepts> synopsis [concepts.syn]"),[<coroutine>](coroutine.syn#header:%3ccoroutine%3e "17.13.2 Header <coroutine> synopsis [coroutine.syn]"),[<format>](format.formatter.spec#header:%3cformat%3e "28.5.6.4 Formatter specializations [format.formatter.spec]"),[<latch>](latch.syn#header:%3clatch%3e "32.9.2.2 Header <latch> synopsis [latch.syn]"),[<numbers>](numbers.syn#header:%3cnumbers%3e "29.8.1 Header <numbers> synopsis [numbers.syn]"),[<ranges>](ranges.syn#header:%3cranges%3e "25.2 Header <ranges> synopsis [ranges.syn]"),[<semaphore>](semaphore.syn#header:%3csemaphore%3e "32.8.2 Header <semaphore> synopsis [semaphore.syn]"),[<source_location>](source.location.syn#header:%3csource_location%3e "17.8.1 Header <source_­location> synopsis [source.location.syn]"),[<span>](span.syn#header:%3cspan%3e "23.7.2.1 Header <span> synopsis [span.syn]"),[<stop_token>](thread.stoptoken.syn#header:%3cstop_token%3e "32.3.2 Header <stop_­token> synopsis [thread.stoptoken.syn]"),[<syncstream>](syncstream.syn#header:%3csyncstream%3e "31.11.1 Header <syncstream> synopsis [syncstream.syn]"), and[<version>](version.syn#header:%3cversion%3e "17.3.2 Header <version> synopsis [version.syn]")[.](#1.sentence-3)

Valid C++ 2017 code that #includes headers with these names may be
invalid in this revision of C++[.](#1.sentence-4)

[2](#2)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/compatibility.tex#L1355)

**Affected subclause:** [[headers]](headers)  


**Change:** Remove vacuous C++ header files[.](#2.sentence-1)

  


**Rationale:** The empty headers implied a false requirement to achieve C compatibility with the C++ headers[.](#2.sentence-2)

  


**Effect on original feature:** A valid C++ 2017 program that #includes any of the following headers may fail to compile:<ccomplex>,<ciso646>,<cstdalign>,<cstdbool>, and<ctgmath>[.](#2.sentence-3)

To retain the same behavior:

- [(2.1)](#2.1)

a #include of <ccomplex> can be replaced by
a #include of [<complex>](complex.syn#header:%3ccomplex%3e "29.4.2 Header <complex> synopsis [complex.syn]"),

- [(2.2)](#2.2)

a #include of <ctgmath> can be replaced by
a #include of [<cmath>](cmath.syn#header:%3ccmath%3e "29.7.1 Header <cmath> synopsis [cmath.syn]") and
a #include of [<complex>](complex.syn#header:%3ccomplex%3e "29.4.2 Header <complex> synopsis [complex.syn]"),
and

- [(2.3)](#2.3)

a #include of<ciso646>,<cstdalign>, or<cstdbool> can simply be removed[.](#2.sentence-4)