Iso C++ Standard Draft

Where do I find the current C or C++ standard documents?

PDF versions of the standard

As of ~~1st September 2014~~ March 2022, the best locations by price for the official C and C++ standards documents in PDF seem to be:

C++20 – ISO/IEC 14882:2020: 212 CAD (about $165 US) from csagroup.org
C++17 – ISO/IEC 14882:2017: $90 NZD (about $65 US) from Standards New Zealand
C++14 – ISO/IEC 14882:2014: $90 NZD (about $65 US) from Standards New Zealand
C++11 – ISO/IEC 14882-2011: $60 from ansi.org or $60 from Techstreet
C++03 – INCITS/ISO/IEC 14882:2003: $30 from ansi.org
C++98 – ISO/IEC 14882:1998: $95 NZD (about $65 US) from Standards New Zealand
C17/C18 – INCITS/ISO/IEC 9899:2018: $116 from INCITS/ANSI / N2176 / c17_updated_proposed_fdis.pdf draft from November 2017 (Link broken, see Wayback Machine N2176)
C11 – ISO/IEC 9899:2011: $60 from ansi.org / WG14 draft version N1570
C99 – INCITS/ISO/IEC 9899-1999(R2005): $60 from ansi.org / WG14 draft version N1256
C90 – ISO/IEC 9899:1990: $90 NZD (about $65 USD) from Standards New Zealand

Non-PDF electronic versions of the standard

Warning: most copies of standard drafts are published in PDF format, and errors may have been introduced if the text/HTML was transcribed or automatically generated from the PDF.

C89 – Draft version in ANSI text format: (https://web.archive.org/web/20161223125339/http://flash-gordon.me.uk/ansi.c.txt)
C89 – Draft version as HTML document: (http://port70.net/~nsz/c/c89/c89-draft.html)
C90 TC1; ISO/IEC 9899 TCOR1, single-page HTML document: (http://www.open-std.org/jtc1/sc22/wg14/www/docs/tc1.htm)
C90 TC2; ISO/IEC 9899 TCOR2, single-page HTML document: (http://www.open-std.org/jtc1/sc22/wg14/www/docs/tc2.htm)
C99 – Draft version (N1256) as HTML document: (http://port70.net/~nsz/c/c99/n1256.html)
C11 – Draft version (N1570) as HTML document: (http://port70.net/~nsz/c/c11/n1570.html)
C++11 – Working draft (N3337) as plain text document: (http://port70.net/~nsz/c/c%2B%2B/c%2B%2B11_n3337.txt)

(The site hosting the plain text version of the C++11 working draft also has some C++14 drafts in this format. But none of them are copies of the final working draft, N4140.)

Print versions of the standard

Print copies of the standards are available from national standards bodies and ISO but are very expensive.

If you want a hardcopy of the C90 standard for much less money than above, you may be able to find a cheap used copy of Herb Schildt's book The Annotated ANSI Standard at Amazon, which contains the actual text of the standard (useful) and commentary on the standard (less useful - it contains several dangerous and misleading errors).

The C99 and C++03 standards are available in book form from Wiley and the BSI (British Standards Institute):

C++03 Standard on Amazon
C99 Standard on Amazon

Standards committee draft versions (free)

The working drafts for future standards are often available from the committee websites:

C++ committee website
C committee website

If you want to get drafts from the current or earlier C/C++ standards, there are some available for free on the internet:

For C:

ANSI X3.159-198 (C89):
I cannot find a PDF of C89, but it is almost the same as C90. The only major differences are in the boilerplate and section numbering, although there are some slight textual differences
ISO/IEC 9899:1990 (C90):
(Almost the same as ANSI X3.159-198 (C89) except for the frontmatter and section numbering. There is at least one textual difference in section 6.5.7 (previously 3.5.7), where "a list" became "a brace-enclosed list". Note that the conversion between ANSI and ISO/IEC Standard is seen inside this document, the document refers to its name as "ANSI/ISO: 9899/99" although this isn't the right name of the later made standard of it, the right name is "ISO/IEC 9899:1990")
TC1 for C90: http://www.open-std.org/jtc1/sc22/wg14/www/docs/n423.pdf
There isn't a PDF link for TC2 on the WG14 website, sadly.
ISO/IEC 9899:1999 (C99 incorporating all three Technical Corrigenda):
http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf
An earlier version of C99 incorporating only TC1 and TC2:
http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1124.pdf
Working draft for the original (i.e. pre-corrigenda) C99: http://www.open-std.org/jtc1/sc22/wg14/www/docs/n843.htm (HTML) and http://www.dkuug.dk/JTC1/SC22/WG14/www/docs/n843.pdf (PDF).
Note that there were two later working drafts: N869 and N878, but they seem to have been removed from the WG14 website, so this is the latest one available.
List of changes between C89/C90 and C99: http://port70.net/~nsz/c/c89/c9x_changes.html
TC1 for C99 (only the TC, not the standard incorporating it): http://www.open-std.org/jtc1/sc22/wg14/www/docs/9899tc1/n32071.PDF
TC2 for C99 (only the TC, not the standard incorporating it): http://www.open-std.org/jtc1/sc22/wg14/www/docs/9899-1999_cor_2-2004.pdf
ISO/IEC 9899:2011 (C11):
http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf
For information on the differences between N1570 and the final, published version of C11, see Latest changes in C11 and https://groups.google.com/g/comp.std.c/c/v5hsWOu5vSw
ISO/IEC 9899:2011/Cor 1:2012 (C11's only technical corrigendum): This can be viewed at https://www.iso.org/obp/ui/#iso:std:iso-iec:9899:ed-3:v1:cor:1:v1:en but cannot be downloaded. It is the actual corrigendum, not a draft.
ISO/IEC 9899:2018 (C17/C18):
https://web.archive.org/web/20181230041359if_/http://www.open-std.org/jtc1/sc22/wg14/www/abq/c17_updated_proposed_fdis.pdf (N2176)
C2x work-in-progress - latest working draft as of 7th August 2022 (N3047):
http://www.open-std.org/jtc1/sc22/wg14/www/docs/n3047.pdf

For C++:

ISO/IEC 14882:1998 (C++98):
http://www.lirmm.fr/~ducour/Doc-objets/ISO+IEC+14882-1998.pdf
ISO/IEC 14882:2003 (C++03):
https://cs.nyu.edu/courses/fall11/CSCI-GA.2110-003/documents/c++2003std.pdf
ISO/IEC 14882:2011 (C++11):
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2012/n3337.pdf
ISO/IEC 14882:2014 (C++14):
https://github.com/cplusplus/draft/blob/master/papers/n4140.pdf?raw=true
ISO/IEC 14882:2017 (C++17):
http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2017/n4659.pdf
ISO/IEC 14882:2020 (C++20): https://isocpp.org/files/papers/N4860.pdf
ISO/IEC 14882:2023 (C++23 work-in-progress. Working draft dated March 17 2022): https://open-std.org/JTC1/SC22/WG21/docs/papers/2022/n4910.pdf

Note that these documents are not the same as the standard, though the versions just prior to the meetings that decide on a standard are usually very close to what is in the final standard. The FCD (Final Committee Draft) versions are password protected; you need to be on the standards committee to get them.

Even though the draft versions might be very close to the final ratified versions of the standards, some of this post's editors would strongly advise you to get a copy of the actual documents — especially if you're planning on quoting them as references. Of course, starving students should go ahead and use the drafts if strapped for cash.

It appears that, if you are willing and able to wait a few months after ratification of a standard, to search for "INCITS/ISO/IEC" instead of "ISO/IEC" when looking for a standard is the key. By doing so, one of this post's editors was able to find the C11 and C++11 standards at reasonable prices. For example, if you search for "INCITS/ISO/IEC 9899:2011" instead of "ISO/IEC 9899:2011" on webstore.ansi.org you will find the reasonably priced PDF version.

The site https://wg21.link/ provides short-URL links to the C++ current working draft and draft standards, and committee papers:

https://wg21.link/std11 - C++11
https://wg21.link/std14 - C++14
https://wg21.link/std17 - C++17
https://wg21.link/std20 - C++20
https://wg21.link/std - current working draft (as of May 2022 still points to the 2021 version)

The current draft of the standard is maintained as LaTeX sources on Github. These sources can be converted to HTML using cxxdraft-htmlgen. The following sites maintain HTML pages so generated:

Tim Song - Current working draft - C++11 - C++14 - C++17 - C++20
Eelis - Current working draft

Tim Song also maintains generated HTML and PDF versions of the Networking TS and Ranges TS.

POSIX extensions to the C standard

The POSIX standard (IEEE 1003.1) requires a compliant operating system to include a C compiler. This compiler must in turn be compliant with the C standard, and must also support various extensions defined in the "System Interfaces" section of POSIX (such as the off_t data type, the <aio.h> header, the clock_gettime() function and the _POSIX_C_SOURCE macro.)

So if you've tried to look up a particular function, been informed "This function is part of POSIX, not the C standard", and wondered why an operating system standard was mandating compiler features and language extensions... now you know!

POSIX.1-2001: The System Interfaces section can be downloaded as a separate document from https://mirror.math.princeton.edu/pub/oldlinux/download/c951.pdf. Section 1.7 states that the relevant version of the C standard is C99.
The "Shell and Utilities" section (https://mirror.math.princeton.edu/pub/oldlinux/download/c952.pdf) mandates not only that a C99-compliant compiler should exist, but that it should be invokable from the command line under the name "c99". One way in which this can be implemented is to place a shell script called "c99" in /usr/bin, which calls gcc with the -std=c99 option added to the list of command-line parameters, and blocks any competing standards from being specified.
POSIX.1-2001 had two technical corrigenda, one dated 2002 and one dated 2004. I don't think they're incorporated into the documents as linked above. There's an online HTML version incorporating the corrigenda at https://pubs.opengroup.org/onlinepubs/009695399/ - but I should add that I've had some trouble with the search box and so using Google to search the site is probably your best bet.
There is a paywalled link to download the first corrigendum at https://standards.ieee.org/standard/1003_1-2001-Cor1-2002.html.
There is also a paywalled link for the second at https://standards.ieee.org/standard/1003_1-2001-Cor2-2004.html

There is a draft version of POSIX.1-2008 at http://www.open-std.org/jtc1/sc22/open/n4217.pdf.
POSIX.1-2008 also had two technical corrigenda, the latter of the two being dated 2016. There is an online HTML version of the standard incorporating the corrigenda at https://pubs.opengroup.org/onlinepubs/9699919799.2016edition/ - though, again, I have had situations where the site's own search box wasn't good for finding information.
There is an online HTML version of POSIX.1-2017 at https://pubs.opengroup.org/onlinepubs/9699919799/ - though, again, I recommend using Google instead of that site's searchbox. According to the Open Group website "IEEE 1003.1-2017 ... is a revision to the 1003.1-2008 standard to rollup the standard including its two technical corrigenda (as-is)". Linux manpages describe it as "technically identical" to POSIX.1-2008 with Technical Corrigenda 1 and 2 applied. This is therefore not a major revision and does not change the value of the _POSIX_C_SOURCE macro.

ISO C++ standard draft

For a while, n3291 was available from the obvious URL (just search and replace n3242 with n3291 in the Wikipedia link). But I guess somebody decided that was too close to the final version so it is no longer accessible.

Thus Wikipedia does not link to it because there is nothing to link to.

I did stash away a copy of n3291 while it was available. I have not done an exhaustive search, but there appear to be no substantive changes; only clarifications. For example, section 1.8 (6) of n3242 reads:

Unless an object is a bit-field or a base class subobject of zero
size, the address of that object is the address of the first byte it
occupies. Two distinct objects that are neither bit-fields nor base
class subobjects of zero size shall have distinct addresses.

While the same section of n3291 reads:

Unless an object is a bit-field or a base class subobject of zero
size, the address of that object is the address of the first byte it
occupies. Two objects that are not bit-fields may have the same
address if one is a subobject of the other or if at least one is a
base class subobject of zero size and they are of different types;
otherwise, they shall have distinct addresses.

(n3291 uses red strike-through and underlined blue text to highlight changes from n3242, so it was not hard to find this example.)

If someone can make a convincing argument that it would be legal for me to re-publish n3291, I would be happy to make it available. I certainly did not have to enter any password or even click on an agreement before downloading it...

[Update: In my first version of this answer, I wrote "n3290" when I meant "n3291". Kind of weird that the "working draft" has a higher number than the "final version". Anyway, what was freely available for a while was n3291.]

[Update 2: N3337 is an initial draft of the next C++ standard, and it is very similar to the C++11 final standard. See:

Do section numbers differ between the C++11 standard and the gratis draft N3337?

So you have your choice of free drafts; the last one before the official standard (N3242), and the first one after it (N3337). All appear to use the same paragraph numbering.]

Where can one find the C89/C90 standards in PDF format?

You can find nice HTML versions of C89, C99, and C11, as well as some of the official draft PDF files they're generated from, here:

http://port70.net/~nsz/c/

Some other useful direct links to free PDF files of the C89/C90, C99 and C11 standards are listed below:

C89/C90: https://www.pdf-archive.com/2014/10/02/ansi-iso-9899-1990-1/ansi-iso-9899-1990-1.pdf

C99:
http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf

C11:
http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf

C11 Standard docs

I finally got answers from:

Ansi

The ISO/IEC 9899:2011 is the original ISO standard published by ISO.

The INCITS/ISO/IEC 9899-2012 is the domestic U.S. adoption of the ISO.
INCITS

Technically, the two standards are identical. The US version has additional front matter to add a U.S. cover and adoption date details. Once we adopt the international standard, we can set the price based on our fee schedule, which generally results in a lesser fee than buying the ISO version.

To provide more background on this, most INCITS technical committees hold U. S. Technical Advisory Group (TAG) relationships to ISO/IEC JTC 1 subcommittees and working groups and, to some ISO technical committees, subcommittees and working groups.

Subject to a few exceptions, INCITS adopts all ISO/IEC or ISO standards that fall within its program of work as “Identical” American National Standards in accordance with the ANSI “Expedited Procedures for the Identical Adoption of an ISO or IEC standard as an American National Standard”.

Similarly, INCITS will generally withdraw any such adopted American National Standard that has been withdrawn as an ISO/IEC or ISO International Standard.

how to read c++ iso standard? i mean the way

The requirements for std::unordered_map are listed in C++20 draft in section 22.2.7. The requirements for Hash are stated in 22.2.7.1.3 as:

Each unordered associative container is parameterized by Key, by a function object type Hash that meets the Cpp17Hash requirements ([hash.requirements]) and acts as a hash function for argument values of type Key, and by a binary predicate Pred that induces an equivalence relation on values of type Key.
Additionally, unordered_map and unordered_multimap associate an arbitrary mapped type T with the Key.

With [hash.requirements] being in 16.4.4.5 section of this standard.

Pred requirements are in 22.2.7.1.5:

Two values k1 and k2 are considered equivalent if the container's key equality predicate pred(k1, k2) is valid and returns true when passed those values.
If k1 and k2 are equivalent, the container's hash function shall return the same value for both.

In general, looking up different requirements in standard is infeasible (unless you are working on a compiler or a resource based on standard like cppreference). It is not really meant for that, because it must be a legal document which takes into account every possibility. I suggest using cppreference instead. Going from page std::unordered_map we can see that it must meet UnorderedAssociativeContainer requirements, which direct us to pages about Hash requirement and to BinaryPredicate requirement.

HTML version of C standard draft (n1256.pdf)?

It seems to be the last draft prior to standardization, rather than C99+TC3, but here's an excellent copy:

http://busybox.net/~landley/c99-draft.html

Edit: And here is C99+TC3: http://port70.net/~nsz/c/c99/n1256.html

And the C11 draft: http://port70.net/~nsz/c/c1x/n1570.html

Which PDF of the C++ ISO standard should I read?

2018 Update: The C++ standard is maintained on GitHub. You can find an archive of old working drafts here that goes back a few years.

The official C++11 standard INCITS/ISO/IEC 14882:2011 is available at ansi.org for $30. You can Google older standards by searching for e.g. 14882:2003 and looking for PDFs. I'm not sure if it's "legal" to download them, so be sure to feel bad about it if you do so.

Before a standard is published, the committee maintains a Working Draft of the standard document with all the revisions as they introduce them. That Working Draft is eventually voted to become a standard, after which only minor editorial changes are made before it is published as a standard.

The working drafts - and quite a few other papers - are released as a numbered series of documents by the committee and are publicly available except for the final approved draft of the standard. ISO rules keep the last revision "secret" so that people will pay for the standard and that money can be used to fund the organizational work the actual ISO does.

People who don't want to pay for the standard use the final public copy of the working draft as a reference, as it is generally identical to the standard document modulo the minor editorial changes I mentioned earlier. For C++11, that last draft is N3242 - Working Draft, Standard for Programming Language C++. The first working draft after C++11 N3337 may more correctly reflect the final standard (I'm too lazy to compare).

The current Working Draft for C++1y is N3690 - Programming Language, C++. If you're really hardcore, you can track the editor's repo of the current draft at Github.