Difference between revisions of "Talk:Main Page/suggestions"

Revision as of 15:15, 20 May 2019

This page collects edit suggestions from new and logged-out users when editing is temporarily disabled due to vandalism. Click the "+" at the top to leave a message. Please make sure to include a link to the page you are referencing. See /archive for old suggestions that have been responded to.

noexcept specifier

The description of functions with an implicit non-throwing exception specifier is not complete. Implicitly declared constructors and assignment operators are omitted. Also comparison operators that are defaulted on their first declaration is omitted. Furthermore it unnecessarily lists categories of constructors and assignment operators.

✔ Done (more precise wording might be required) The categories is listed because they link to different pages. Fruderica (talk) 20:39, 21 April 2019 (PDT)

Expression SFINAE DR339 / N2634

I would like to add Expression SFINAE as a C++11 feature: N2634

Supported in: GCC 4.4, clang 2.9, MSVC: no/partial support. In particular, no support for decltype [temp.deduct]/7 up to 19.15. source

Rustyx (talk) 12:40, 22 February 2019 (PST)

what's missing from its current description in cpp/language/sfinae#Expression_SFINAE? --Cubbi (talk) 12:46, 22 February 2019 (PST)

I think Rustyx means to add a new row in cpp/compiler support. T. Canens (talk) 10:02, 23 February 2019 (PST)

Indeed that's what I meant, cpp/compiler support. Can't post on that page, unfortunately. Rustyx (talk) 10:48, 24 February 2019 (PST)

Added (partially). I don't know whether IBM XL C++, Sun/Oracle C++ or HP aCC support expression SFINAE, or in which edition they began to support. If anyone knows, please improve it. --Fruderica (talk) 03:57, 25 April 2019 (PDT)

Permission for editing: Compiler support

I would like to add the Apple Clang/Xcode column to the compiler support page now. Thanks in advance for permissions.--Buovjaga (talk) 02:25, 23 February 2019 (PST)

I don't think I have the technical ability to manually grant permissions. If you post the edits here, I can copy them over. (Although by the time you are done posting them here you may well have accumulated enough edits to get past the threshold...) T. Canens (talk) 10:00, 23 February 2019 (PST)

I gave this a lot of thought, but I am afraid I cannot bring myself to do it. The work will require possibly creating multiple templates. I cannot reason about this in theory, I need to be able to see the effects of the templates live. Even if I could, I would essentially be writing a complex tutorial on doing the edits, which seems like a massive waste of effort. I will be waiting for the editing permissions. Buovjaga (talk) 05:49, 3 March 2019 (PST)

After more thought, I will attempt to describe what should be done. I hope someone can pick this up. The goal is to create a new column named Apple Clang, perhaps after the existing Clang column. It would contain the Apple Clang version number and show the Xcode version number in a tooltip (hint). Steps below:

1. Add the column to Template:compiler_support_row and Template:compiler_support_top
2. Possibly add a new template in the style of Template:msvc_ver. I don't know the best way to design it so it would accept the Apple Clang and Xcode versions.
3. In the actual article, add "yes" entries for std::any, std::variant and std::optional with Apple Clang version 10.0.0 and Xcode version 10.0
4. Add a "no" entry for std::filesystem
5. Add to references: https://en.wikipedia.org/wiki/Xcode#Toolchain_versions and https://developer.apple.com/documentation/xcode_release_notes/xcode_10_release_notes

--Buovjaga (talk) 05:37, 19 March 2019 (PDT)

I think you have enough edits now to get past the threshold and make the edits directly, just FYI. T. Canens (talk) 20:58, 19 March 2019 (PDT)

new expression missing exception specs

Somewhere way down in that wall of text there is a mention of std::bad_array_new_length, but that's it. I think there should be a dedicated section "Exceptions" (as in other docs on this site) documenting std::bad_alloc and std::bad_array_new_length as well as the non-throwing versions, as this is pretty fundamental. Perhaps also an example.

Thanks! 213.68.42.195 03:02, 25 February 2019 (PST)

New user

Hello, I would like to make changes to the C++ compiler support page related to the addition of the "Modules" and "Coroutines" features to C++20. Can somebody give me permissions to edit or otherwise do the changes as per the following articles:

https://www.phoronix.com/scan.php?page=news_item&px=Coroutines-Modules-CPP20 https://herbsutter.com/2019/02/23/trip-report-winter-iso-c-standards-meeting-kona/

--Trifud (talk) 23:15, 26 February 2019 (PST)

How long time does it take for a user to be activated? --Trifud (talk) 23:09, 28 February 2019 (PST)

RFC: another implementation of Gadget-StandardRevision

(function() {
'use strict';
var styles = document.createElement('style');
styles.textContent = '[hidden] { display: none !important; }';
styles.textContent += '.stdrev-rev-hide > tbody > tr > td { border: none !important; padding: 0 !important; }'
styles.textContent += '.stdrev-rev-hide > tbody > tr > td:nth-child(2) { display: none; }'
styles.textContent += '.stdrev-rev-hide { border: none; }'
styles.textContent += '.stdrev-rev-hide > span > .t-mark-rev { display: none; }'
document.head.append(styles);
 
var rev = mw.config.get('wgTitle').indexOf('c/') === 0 ?
	[ 'C89', 'C99', 'C11' ] :
	[ 'C++98', 'C++03', 'C++11', 'C++14', 'C++17', 'C++20' ];
 
var select = $('<div class="vectorMenu"></div>').appendTo('#cpp-head-tools-right');
select.append('<h5><span>Std rev</span></h5>');
var list = $('<ul>').appendTo($('<div class="menu">').appendTo(select));
$.each(['DIFF'].concat(rev), function(i, v) {
	list.append('<li><a href="#'+v+'">'+v+'</a></li>');
});
list.on('click', 'a', function(e) {
	list.find('a').css('font-weight', 'normal');
	$(this).css('font-weight', 'bold');
	curr_rev = e.target.innerText;
	on_rev_changed();
});
 
var curr_rev = 'DIFF';
 
// Returns true if an element should be shown in the current revision, that is, either curr_rev is
// DIFF (i.e. show all), or curr_rev is within the range [since, until). The range [since, until)
// is inspected from the classes of `el`.
// `el` may be the same element as the one to be shown if it has the needed classes, or it may be a
// revision marker or a collection thereof (e.g. one expanded from {{mark since foo}}, or from the
// {{mark since foo}}{{mark until bar}} combo).
// `el` may be either a HTML element or a jQuery object.
// Note that this correctly handle the case when `el` represents an empty set of elements (in which
// case the element is always shown).
function should_be_shown(el) {
	if (curr_rev === 'DIFF') return true;
	var curr_revid = rev.indexOf(curr_rev);
	var since = 0, until = rev.length;
	$.each(rev, function(i) {
		var ssince = 't-since-'+rev[i].toLowerCase().replace(/\+/g, 'x');
		var suntil = 't-until-'+rev[i].toLowerCase().replace(/\+/g, 'x');
		if ($(el).hasClass(ssince)) since = i;
		if ($(el).hasClass(suntil)) until = i;
	});
	return since <= curr_revid && curr_revid < until;
}
 
// Called when user changes the selected revision. Inside this function, curr_rev is already set to
// the value after the change.
function on_rev_changed() {
	handle_dcl();
	renumber_dcl();
	handle_dsc();
	handle_nv();
	handle_rev();
	handle_headings();
	handle_list_items();
	$('.t-rev-begin, .t-rev-inl').toggleClass('stdrev-rev-hide', curr_rev !== 'DIFF');
	$('.t-mark-rev').each(function() {
		this.hidden = curr_rev !== 'DIFF';
		if ($(this.nextSibling).is('br'))
			this.nextSibling.hidden = curr_rev !== 'DIFF';
	});
}
 
// Returns true if the jQuery object `el` contains at least one element, and all contained elements
// are hidden; otherwise returns false.
// This is used to hide a 'parent' or 'heading' element when all its contents are hidden.
function all_hidden(el) { return $(el).length > 0 && !$(el).is(':not([hidden])'); }
 
// Hide or show the elements expanded from the {{dcl ...}} template family. See documentation at
// https://en.cppreference.com/w/Template:dcl/doc .
// The dcl items (expanded from {{dcl | ... }}) may either appear alone or as children of versioned
// declaration list (expanded from {{dcl rev begin | ... }}). In the latter case, the revision may
// be supplied by the dcl items or by the dcl-rev (in the latter case the dcl-rev has class
// t-dcl-rev-notes).
// For the use of renumber_dcl(), each dcl-rev is marked as hidden if all its children dcl items
// are hidden, and vice versa.
function handle_dcl() {
	$('.t-dcl').each(function() {
		this.hidden = !should_be_shown(this);
	});
	$('.t-dcl-rev').each(function() {
		if ($(this).is('.t-dcl-rev-notes')) {
			var hidden = !should_be_shown(this);
			this.hidden = hidden;
			$(this).find('.t-dcl').each(function() {
				this.hidden = hidden;
			});
		} else {
			this.hidden = all_hidden($(this).find('.t-dcl'));
		}
	});
	$('.t-dcl-begin .t-dsc-header').each(function() {
		var marker = $(this).find('> td > div > .t-mark-rev');
		var lastheader = $(this).nextUntil(':not(.t-dsc-header)').addBack();
		var elts = lastheader.nextUntil('.t-dsc-header').filter('.t-dcl, .t-dcl-rev');
		this.hidden = all_hidden(elts) || !should_be_shown(marker);
	});
	$('.t-dcl-h').each(function() {
		this.hidden = all_hidden($(this).nextUntil(':not(.t-dcl, .t-dcl-rev)'));
	});
}
 
// Ensure that each visible dcl item in a dcl list is contiguously numbered, and rewrite mentions
// to these numbers to use the modified numbering.
// If a list item (e.g. those expanded from @m@) contains no number after the rewrite (i.e. it's
// inapplicable in current revision), it is hidden.
// Note that the use of '~ * .t-li, ~ * .t-v' effectively establishes a kind of scoping: only
// numbers that appear after the dcl list and are more nested in the DOM hierarchy are affected
// by the renumbering.
// Requires that handle_dcl() has been called.
function renumber_dcl() {
	$('.t-dcl-begin').each(function() {
		var numbering_map = [];
		var i = 0;
		$(this).find('.t-dcl, .t-dcl-rev').each(function() {
			var num_cell;
			if ($(this).is('.t-dcl'))
				num_cell = $(this).children('td:nth-child(2)');
			else
				num_cell = $(this).find('> tr.t-dcl-rev-aux > td:nth-child(2)');
			var number_text = /\s*\((\d+)\)\s*/.exec(num_cell.text());
			if (!num_cell.attr('data-orig-num') && number_text)
				num_cell.attr('data-orig-num', number_text[1]);
			var original_num = num_cell.attr('data-orig-num');
			if (original_num) {
				if (! numbering_map[original_num])
					numbering_map[original_num] = $(this).is('[hidden]') ? null : ++i;
				num_cell.text('('+numbering_map[original_num]+')');
			}
		});
		$(this).find('~ * .t-li, ~ * .t-v').each(function() {
			if (! $(this).attr('data-orig-v'))
				$(this).attr('data-orig-v', $(this).text().replace(/[()]/g, ''));
			var original_numbers = [];
			$.each($(this).attr('data-orig-v').split(','), function(i, v) {
				var match = /(\d+)(?:-(\d+))?/.exec(v);
				if (match[2])
					for (var i = +match[1]; +i <= +match[2]; ++i)
						original_numbers.push(i);
				else
					original_numbers.push(match[1]);
			});
			var numbers = $.map(original_numbers, function(x) {
				return numbering_map[x];
			});
			var s = [];
			for (var i = 0; i < numbers.length; ++i) {
				if (numbers[i+1] - numbers[i] === 1 && numbers[i+2] - numbers[i+1] === 1) {
					var begin = numbers[i];
					while (numbers[i+1] - numbers[i] === 1)
						++i;
					s.push(begin+'-'+numbers[i]);
				} else {
					s.push(numbers[i]);
				}
			}
			if ($(this).is('.t-li')) {
				this.parentElement.hidden = numbers.length === 0;
				$(this).text(s.join(',')+')');
			} else
				$(this).text('('+s.join(',')+')');
		});
	});
}
// Hide or show the elements expanded from the {{dsc ...}} template family. See documentation at
// https://en.cppreference.com/w/Template:dcl/doc .
// The revision markers are in the first cell of each dsc item. In the general case, the visibility
// of a dsc item is control by a single revision marker. But if a specialized template is used,
// and the amount of entity names in the first cell matches the lines of the revision markers,
// then each line controls the visibility of a single entity name, and the dsc item is hidden only
// if all the entity names are hidden.
// If all the dsc items are hidden, then the corresponding headings are hidden as well.
function handle_dsc() {
	$('.t-dsc').each(function() {
		var member = $(this).find('.t-dsc-member-div');
		if (member[0]) {
			var lines = member.find('> div:nth-child(2) > .t-lines').children();
			var mems = member.find('> div:first-child .t-lines').children();
			if (lines.length !== mems.length)
				this.hidden = !should_be_shown(lines.children('.t-mark-rev'));
			else {
				lines.each(function(i) {
					var marker = $(this).children('.t-mark-rev');
					mems[i].hidden = !should_be_shown(marker);
					marker.hidden = !should_be_shown(marker);
				});
				this.hidden = all_hidden(mems);
			}
		} else {
			var marker = $(this).find('> td:first-child > .t-mark-rev');
			this.hidden = !should_be_shown(marker);
		}
	});
	$('.t-dsc .t-dsc-header').each(function() {
		var marker = $(this).find('> td > div > .t-mark-rev');
		var lastheader = $(this).nextUntil(':not(.t-dsc-header)').addBack();
		this.hidden = all_hidden(lastheader.nextUntil(':not(.t-dsc)')) || !should_be_shown(marker);
	});
	var heading_selector = ['tr:has(> td > h5)', 'tr:has(> td > h3)'];
	$.each(heading_selector, function(i, selector) {
		$(selector).each(function() {
			var section = $(this).nextUntil(heading_selector.slice(i).join(','));
			this.hidden = all_hidden(section.filter('.t-dsc'));
		});
	});
	$('.t-dsc-begin').each(function() {
		this.hidden = all_hidden($(this).find('.t-dsc'));
	});
}
// Hide or show the navbar elements expanded from the {{nv ...}} template family. See documentation
// at https://en.cppreference.com/w/Template:nv/doc .
// A line of revision marker only controls a single entity name, even if it's expanded from
// {{nv ln | ... }} that contains multiple lines.
// If a heading contains a revision marker, that revision marker controls the visibility of the
// heading and its corresponding contents; otherwise the heading is hidden when it is followed by
// content elements, and all of them are hidden.
function handle_nv() {
	$('.t-nv').each(function() {
		var marker = $(this).find('> td > .t-mark-rev');
		this.hidden = !should_be_shown(marker);
	});
	$('.t-nv-ln-table').each(function() {
		var lines = $(this).find('> div:nth-child(2) > .t-lines').children();
		var mems = $(this).find('> div:first-child .t-lines').children();
		lines.each(function(i) {
			var marker = $(this).children('.t-mark-rev');
			if (mems[i]) mems[i].hidden = !should_be_shown(marker);
			marker.hidden = !should_be_shown(marker);
		});
		this.hidden = all_hidden(mems);
	});
	var heading_selector = ['.t-nv-h2', '.t-nv-h1'];
	$.each(heading_selector, function(i, selector) {
		$(selector).each(function() {
			var section = $(this).nextUntil(heading_selector.slice(i).join(','));
			var marker = $(this).find('> td > .t-mark-rev');
			if (marker[0]) {
				section.each(function() {
					this.hidden = this.hidden || !should_be_shown(marker);
				});
				this.hidden = !should_be_shown(marker);
			}
			this.hidden = all_hidden(section.find('.t-nv-ln-table'));
		});
	});
}
// Hide or show the elements expanded from the {{rev ...}} template family. See documentation at
// https://en.cppreference.com/w/Template:dcl/doc .
// Borders are handled by class stdrev-rev-hide.
function handle_rev() {
	$('.t-rev, .t-rev-inl').each(function() {
		this.hidden = !should_be_shown(this);
	});
}
// Hide or show headings.
// If the heading contains a revision marker, that revision marker controls the visibility of it
// and its corresponding contents; otherwise, a heuristic is made: if the contents contain a dsc
// list, and its revision-related contents are hidden, then the heading and all contents are hidden
// as well.
// The heuristic requires that handle_dsc() and handle_rev() have been called.
function handle_headings() {
	var heading_selector = ['h5', 'h4', 'h3', 'h2'];
	$.each(heading_selector, function(i, selector) {
		$(selector).each(function() {
			var section = $(this).nextUntil(heading_selector.slice(i).join(','));
			var marker = $(this).find('> span > .t-mark-rev');
			if (marker[0]) {
				section.each(function() {
					this.hidden = this.hidden || !should_be_shown(marker);
				});
				this.hidden = !should_be_shown(marker);
			}
			if (section.is('.t-dsc-begin') && !section.is(':not(p, .t-rev-begin, .t-dsc-begin)')) {
				var revisioned_content = section.find('.t-dsc, .t-rev, .t-rev-inl');
				section.each(function() {
					this.hidden = this.hidden || all_hidden(revisioned_content);
				});
				this.hidden = all_hidden(revisioned_content);
			}
		});
	});
}
// Hide or show <li> elements based on the contained revision markers.
function handle_list_items() {
	$('li').each(function() {
		var marker = $(this).children('.t-mark-rev');
		this.hidden = !should_be_shown(marker);
	});
}
})();

Features include:

1. hide section based on revision markers in the heading
2. hide <li> based on its contained revision markers
3. hide "Defined in header ..." when the corresponding entities are hidden
4. implement renumbering inside {{v}}
5. much shorter than P12's implementation! (~300LOC vs ~1800LOC)

Does it make sense to include this as an "official" gadget?

--223.3.167.101 10:25, 3 March 2019 (PST)

We don't want to have two gadgets for the same thing. What does the current gadget do that this script doesn't, and vice versa? What caused the drastic shortening? T. Canens (talk) 11:07, 23 March 2019 (PDT)

> What does the current gadget do that this script doesn't

1. be hosted on GitHub

2. have tests

With regard to functionality, I don't know of any case that is handled better by Gadget-StandardRevision than by this script, but I don't have a thorough test.

> and vice versa?

All features mentioned above. Also, it does not have the problem reported below: Gadget-StandardRevision ignores all except the first revision marker in a row, and behaves unintuitively when the markers occupy more rows than the names in the dsc item. This script takes care to handle these cases better.

> What caused the drastic shortening?

Gadget-StandardRevision clones each of the elements that may be affected by the Gadget, and has a complex data structure to keep track of these elements and their clones. A lot of work is done to construct, manipulate, and debug this data structure. By contrast, this implementation directly manipulates the affected elements, which requires much less lines of code.

--121.249.15.21 10:52, 24 March 2019 (PDT)

The current gadget is also hosted on GitHub and has tests https://github.com/p12tic/cppreference-doc --Ybab321 (talk) 10:30, 26 March 2019 (PDT)

Right, so I listed it as a thing that the current gadget do that this script doesn't :) --121.249.15.75 11:38, 26 March 2019 (PDT)

Oops, my mistake :( --Ybab321 (talk) 06:44, 31 March 2019 (PDT)

Search: noreturn - does not find en.cppreference.com/w/cpp/language/attributes/noreturn

How can I update the search system?

Several times I have searched for terms & not found them only to Google them & be given a cppreference page.

Also `Search: fallthrough` does not find en.cppreference.com/w/cpp/language/attributes/fallthrough.

And `Search: if constexpr` does not find en.cppreference.com/w/cpp/language/if.

I’m sure that there are more ...

Chris0 (talk) 18:50, 5 March 2019 (PST)

Updating the Embarcadero column

I'm a newly registered user, so cannot edit this page as it's under protection.

The Embarcadero column for C++14 and C++17 is out of date. The compiler supports all of C++14, and all of C++17 bar:

• Replacement of class objects containing reference members P0137R1
• Standardization of Parallelism TS P0024R2
• Elementary string conversions P0067R5
• Splicing Maps and Sets P0083R3
• Hardware interference size P0154R1

More info here: http://docwiki.embarcadero.com/RADStudio/Rio/en/Modern_C%2B%2B_Language_Features_Compliance_Status#C.2B.2B14_Features and http://docwiki.embarcadero.com/RADStudio/Rio/en/Modern_C%2B%2B_Language_Features_Compliance_Status#C.2B.2B17_Features

yes, their new compilers are basically Clang: Embarcadero 10.1 is Clang 3.3, Embarcadero 10.3 (linked above) is Clang 5.0. But I suppose it's fair to update the table (for now, I updated the links below the table) --Cubbi (talk) 06:40, 8 March 2019 (PST)

Standard Revision gadget problems with C++20

It seems there are some problems with displaying (not displaying) features removed in C++20, On std::allocator page choosing C++20 Standard to be displayed, every removed feature is still on the list, marked as deprecated, information "removed in C++20" disappears. Is this template problem or widget problem? Kaznov (talk) 09:38, 15 March 2019 (PDT)

Shall we clarify on copy functions of standard exception classes?

It seems that the existence and the postcondition of copy functions of standard exception classes (exception/2) are not mentioned in cppreference. --Fruderica (talk) 02:33, 31 March 2019 (PDT)

inconsistent capitalization

In https://en.cppreference.com/w/cpp/atomic/memory_order "thread 1" is capitalized inconsistently in the text description of the relaxed ordering - sometimes it's "thread 1", sometimes "Thread 1". Same for "thread 2".

Thanks, Dan 109.66.82.93 10:20, 31 March 2019 (PDT)

✔ Done Use lowercase consistently. Fruderica (talk) 18:23, 21 April 2019 (PDT)

sizeof parameter can't be a C-style cast

I'm not able to make this change, but would like to suggest it.

sizeof's notes ought to say something like:

With form (2), expression cannot be a C-style cast, due to ambiguity with form (1). In other words, sizeof (char)+1 is parsed as (sizeof(char)) + 1, rather than sizeof((char)+1). — Preceding unsigned comment added by Myria (talk • contribs)

std::sort() should mention strict weak ordering requirements

The description of std::sort() does not mention that the comparison operator comp must define a strict weak ordering. Unless the standard has changed, it is undefined behavior to sort with a comparison function which does not define a strict weak ordering.

It also is probably worthwhile to explicitly point out that sorting with a comparison function that does not define a strict weak ordering is undefined behavior, and in fact in common implementations can lead to a crash or infinite loop, since it's a really commonly-encountered pitfall.

It may also be worthwhile pointing out that operator< does *not* define a strict weak ordering over floating point values due to NaN behavior, and so std::sort() may crash when applied to a vector of floating point values.

I believe that std::stable_sort() has implementation defined behavior rather than undefined when there's not a strict weak ordering, so it might also be worthwhile recommending using std::stable_sort() in such cases.

SethML (talk) 10:41, 9 April 2019 (PDT)

cpp/algorithm/sort says "Compare must meet the requirements of Compare." and cpp/named_req/Compare explains strict weak ordering and all other requirements on the comparison function. I suppose it could be highlighted, something like "must meet the requirements of Compare, including the strict weak ordering requirement", but then it sounds like there are cases where the ordering is not included. Maybe a concise bad example would be worth adding.

As for stable_sort, the actual requirement uses the word of power "shall"], so it's undefined to violate that for both sort and stable_sort. --Cubbi (talk) 11:12, 9 April 2019 (PDT)

Indeed, I've been reading the standards and discovering these things. I'd had this assumption that stable_sort() was implementation-defined over poorly-ordered sequences, but it appears that it's actually undefined and could crash. In practice I think most implementations are a merge sort, which should have some reasonable behavior given input which isn't strict weak ordered. But the standard doesn't guarantee that, sadly.

The phrasing in the standard is: For algorithms other than those described in alg.binary.search, comp shall induce a strict weak ordering on the values.

I'd missed that the Compare requirement encoded the strict weak ordering requirement - that's pretty subtle. I do think that for all of the sort functions, it'd be nice to expand the compare bullet point, something like:

* Compare must meet the requirements of Compare, including the strict weak ordering requirement. If it doesn't the behavior of X_sort is undefined.

A bad example using floating point could be a good way to call out UB with floating point collections, since that's a serious gotcha.

I find it also an interesting question what the behavior of lower_bound and friends is if passed a sequence that is not partitioned with respect to the value being searched for. The standard does not use the word "shall" - it says: All of the algorithms in this subclause are versions of binary search and assume that the sequence being searched is partitioned with respect to an expression formed by binding the search key to an argument of the comparison function. What is your interpretation of the result if the sequence is not partitioned - undefined behavior, or implementation defined?

"implementation-defined" is an additional standard requirement, not made here. I would say "undefined". If you feel strongly enough about it, consider raising an editorial issue on whether 'assume' in [alg.binary.search]/1 means the same as 'shall' in [alg.sorting]/3, and what does it mean to violate it (ill-formed? undefined? unspecified?) --Cubbi (talk) 06:54, 10 April 2019 (PDT)

Also, if I comment on [Talk:Main_Page/suggestions] enough, will I gain edit access? --SethML (talk) 12:11, 9 April 2019 (PDT)

Suggestion to fix menu

I think in the navigation menu (Template:cpp/language/declarations/navbar_content), "asm-definition" should be replaced by "asm-declaration". --62.46.159.123 00:59, 13 April 2019 (PDT)

The item asm-definition is used by the standard, so it's not necessary to change. --Fruderica (talk) 07:21, 21 April 2019 (PDT)

Definintion of synchronizes-with in cpp/atomic/memory order?

The page cpp/atomic/memory order tries to be fairly formal with defining the different types of memory ordering constraints, but a definition for "synchronizes-with" (which "inter-thread happens-before" depends on) appears to be missing.

more copy & pastable header

On all the pages at the top it says "Defined in <X>". I think it would be better to do "#include <X>" instead so I can copy & paste that into my code directly.

135.23.100.188 12:00, 21 April 2019 (PDT)Ben

search widget takes me to wrong page when searching for restrict

Entering "restrict" into the search widget at the top of the page, takes you to https://en.cppreference.com/w/cpp/memory/gc/get_pointer_safety rather than https://en.cppreference.com/w/c/language/restrict

Not all error_codes are platform-dependent

In https://en.cppreference.com/w/cpp/error error_condition and error_error are described as:

error_condition (C++11) holds a portable error code

error_code (C++11) holds a platform-dependent error code

But that doesn't seem to be correct. See for example https://akrzemi1.wordpress.com/2017/07/12/your-own-error-code/#comment-6921 or http://blog.think-async.com/2010/04/system-error-support-in-c0x-part-2.html

The descriptions are from overviews in the standard, see syserr.errcode.overview and syserr.errcode.overview. If you want to add something about the actual usage, I think we can add a "Notes" section to describe it. (By the way, the second article was written before C++11 so I doubt whether it is useful now.) --Fruderica (talk) 07:45, 27 April 2019 (PDT)

open source libs

How to add reference to open source lib? (Alex25 (talk) 01:20, 28 April 2019 (PDT))

Improving this site

I'm hardly a new user... can't I get edit rights (back)? CarloWood (talk) 09:18, 28 April 2019 (PDT)

precision() and width() of ios_base

The descriptions of the second overloads do not mention returning the previous value as is done for instance with fill() of basic_ios. — Preceding unsigned comment added by 2a00:23c6:8b1b:d800:59f4:fa4:b8bb:5760 (talk • contribs) 01:20, 2 May 2019

✔ Added. The descriptions of return value are for both overloads. I think there is nothing missing. --Fruderica (talk) 08:04, 2 May 2019 (PDT)

BNFLite

Could you add nice BNFLite parsing h-library ( https://github.com/r35382/bnflite) into Text::Parse section

Language support page: list library support with the library name not the compiler name

The language support page lists compiler names in the list of library features. In a lot of Linux distributions, Clang will by default use GCC's libstdc++ instead of LLVM's libc++, which means that the relevant column to look at in that table for support when using Clang is the GCC column, not the Clang column. Likewise, clang-cl will use MSVC's standard library by default. (I think Intel's compiler behaves similarly to Clang in this regard, and indeed probably several other compilers in the table are not coupled to a particular standard library implementation.)

The current table structure seems less helpful than it could be.

Suggestion: rename the GCC column to libstdc++ and the Clang column to libc++; remove the columns for compilers that don't have their own standard library implementation; add introductory text explaining which standard library each compiler uses by default.

zygoloid (talk) 17:12, 4 May 2019 (PDT)

this has been suggested as far back as 2016 Talk:cpp/compiler_support#Splitting_and_folding the_table and I don't think there is any opposition. Someone just needs to volunteer. --Cubbi (talk) 06:08, 6 May 2019 (PDT)

Now I have placed core language features and library features into different tables, and renamed the columns when listing library features. However I think the introductory might be a hard work, since the compilers' default usage of standard library implementation is not well-documented. --Fruderica (talk) 21:54, 6 May 2019 (PDT)

The given example in "C++ new expression" can't be compiled.

In this page, [1],

The initializer is not optional if

- a placeholder (auto or decltype(auto) (since C++14)) is used in type - type is an array of unknown bound

auto p = new auto('c'); // creates a single object of type char. p is a char* double* p = new double[]{1,2,3}; // creates an array of type double[3]

The last line of code couldn't be compiled with GCC8.1 c++2a, Clang5.0 C++17, which is wired. I searched the net and find nothing related about it.So please confirm if it is a mistake. Thank you.

Array size deduction in new-expressions (P1009R2) is a newly adopted (2019-03) defect report. Currently we don't treat it as a C++20 feature. --Fruderica (talk) 21:37, 6 May 2019 (PDT)

Added to table. T. Canens (talk) 20:56, 12 May 2019 (PDT)

Equivalence of the signature of function objects

Hi,

the documentation of (e.g.) std::accumulate says:

 op The signature of the function should be equivalent to the following:

    Ret fun(const Type1 &a, const Type2 &b);

The signature does not need to have const &.

When is a signature "equivalent" to the above? 2001:B01:2404:4:0:0:0:57 23:49, 9 May 2019 (PDT)

This is handwaving vigorously. The basic requirement is that a set of expressions must work. But of course that's a bit abstract and we want to show what a function (object) that meets the requirement should look like. Hence the weasel-wording. Perhaps we should rephrase the requirements in terms of the required expressions, and then show sample signatures as examples? T. Canens (talk) 20:23, 17 May 2019 (PDT)

MSVC support for P1164

Fruderica, thank you so much for updating the feature table, including the detailed charconv tooltip!

"But this page says that P1164 has been implemented in VS 2019 16.0. Is it implemented or not?"

That's an excellent catch. That page is correct - P1164 is indeed implemented in VS 2019 16.0, toolset 19.20. You've found a mistake in my internal spreadsheet, and in our STL header comments. I'll go fix both (it's a long story, involving us implementing this feature when it was still in draft form, and multiple oversights on my part regarding my spreadsheet).

STL MSFT (talk) 12:39, 10 May 2019 (PDT)

Thanks for replying. I've added P1161R1 to the table. And I think P0600R1 might be considered as partially supported in VS 2017 15.6 (or 15.7?). I've found that all required functions are marked with _NODISCARD except for operator new. --Fruderica (talk) 03:50, 11 May 2019 (PDT)

operator :: – ( I cannot edit https://en.cppreference.com/w/Talk:cpp/language/operator_precedence where it belongs to)

At https://en.cppreference.com/w/cpp/language/operator_precedence the token :: that is used to build nested names is listed as an "operator". But AFAIK this token is not an operator (or a very special one).

Because for any (binary) operator ★ the term A★B★C either means (A★B)★C _or_ A★(B★C) and you might add (…) to change the meaning.

But for :: you can't do this, because A::(B::C) does not compile, and (A::B)::C compiles, but is parsed as a type cast of ::C into the type A::B. :-/

What do you think? Should it be changed or at least mentioned? --Roker (talk) 04:01, 13 May 2019 (PDT)

the whole table is a loose approximation of expression grammar in human-readable terms of "precedence" and "associativity". These terms do not appear anywhere in the language specification, they are invented by the authors of the table. In the expression grammar, :: combines identifiers into primary expressions, so inasmuch as the grammar can be expressed in those terms, it has the "highest precedence". We could drop it, but then people used to seeing precedence tables from other sources such as enwiki:Operators_in_C_and_C++#Operator_precedence would say cppreference's table is incomplete and add it back. --Cubbi (talk) 06:40, 13 May 2019 (PDT)

They can already say that since cppreference's table does not include const_cast et al, though.

OTOH, the standard calls :: an operator in [over.oper]/3. --D41D8CD98F (talk) 11:06, 14 May 2019 (PDT)

Add reference to paragraph about automatically generated class member functions

Hi there.

In https://en.cppreference.com/w/cpp/language/classes, I suggest in the last paragraph we add references to the rule of zero/three/five.

The very last sentence says:

"Some member functions are special: under certain circumstances they are defined by the compiler even if not defined by the user."

This would be an optimal place to refer to the rule of zero/three/five (link: https://en.cppreference.com/w/cpp/language/rule_of_three).

217.10.52.10 05:02, 13 May 2019 (PDT) André Malcher

Help to translate

Eu gostaria de ajudar a traduzir as páginas para o português do Brasil, por que tem grande diferenças do de Portugal.

Gostaria de saber como posso fazer isso?

including cstddef in the std::size_t snippet

Why does the std::size_t code snippet contain #include <cstddef>? If it’s not needed, can we remove it? Thanks. —LLarson (said & done) 09:01, 13 May 2019 (PDT)

that's one of the six headers where std::size_t is guaranteed to be defined, as noted on that same page. Removing it makes a non-portable program. --Cubbi (talk) 09:18, 13 May 2019 (PDT)

However, size_t also appears in synopsis of many other headers in the standard, such as <array>. Is it permitted by the standard that including <array> does not make std::size_t available? --Fruderica (talk) 00:06, 14 May 2019 (PDT)

You may have a point.. but it's probably still better to include what you use explicitly: SF.10 --Cubbi (talk) 06:01, 14 May 2019 (PDT)

Yes. It can spell it decltype(sizeof(0)), for instance. The only thing you are guaranteed to get from including a header is the things actually declared in the synopsis. T. Canens (talk) 06:03, 14 May 2019 (PDT)

Code doesn't build

In https://en.cppreference.com/w/cpp/container/map/find the

   LightKey lk = { 2 };
   auto search2 = example2.find(lk);

doesn't build, because example2 is FatKey not LightKey.

The code demonstrates a C++14 feature. It certainly builds with modern toolchains. --Cubbi (talk) 06:01, 14 May 2019 (PDT)

tuple_element for span

On page tuple_element for span shouldn't the constraint read "The program is ill-formed if I >= N or if N == std::dynamic_extent." instead of I > N?

Xaos (talk) 00:57, 15 May 2019 (PDT)

Yes, fixed, thanks! T. Canens (talk) 05:39, 15 May 2019 (PDT)

Add argument types in the examples

https://en.cppreference.com/w/cpp/io/c/fprintf

Stupidly enough, despite the extensive examples, there is none using the argument types (e.g. %lu)

std::raw_storage_iterator example code does not consider std::get_temporary_buffer quirks

I know this is all stuff that is being removed in C++20, but: in the example in std::raw_storage_iterator it calls std::get_temporary_buffer and goes straight on the returned pointer.

However, std::get_temporary_buffer is a non-binding request that may return less memory than requested, so, before actually using the provided pointer to store the elements, it should check if it actually got enough memory for them.

Cvtsi2sd (talk) 01:47, 17 May 2019 (PDT)

Fixed, thanks! T. Canens (talk) 06:10, 17 May 2019 (PDT)

Add AI TP\O CURRlink title

https://ai.stackexchange.com/questions/6185/why-does-c-seem-less-widely-used-in-ai[2]

Add AI libraries for c++.

https://ai.stackexchange.com/questions/6185/why-does-c-seem-less-widely-used-in-ai[3]

AI using C++...

[ai.stackexchange.com/questions/6185/why-does-c-seem-less-widely-used-in-ai] is the source of the following. I have inserted links to the libraries web sites. You don't need a powerful language for programming AI. Most of the developers are using libraries like Keras,[keras.io] Torch [torch.ch], Caffe,[caffe.berkeleyvision.org] Watson [cloud.ibm.com/developer/watson/dashboard], TensorFlow,[www.tensorflow.org] etc. Those libraries are highly optimized and handle all the though work, they are built with high performance languages, like C. Python is just there to describe the neural network layers, load data, launch the processing and display results. Using C++ instead would give barely no performance improvement, but would be harder for non-developers as it require to care for memory management. Also, several AI people may not have a very solid programming or computer science background.

Another similar example would be game development, where the engine is coded in C/C++, and, often, all the game logic scripted in a high level language. Ian Martin Ajzenszmidt (talk) 05:39, 18 May 2019 (PDT)

c++ for ai bibliography from scholar.google.com

https://scholar.google.com.au/scholar?hl=en&as_sdt=0%2C5&q=c%2B%2B+for++artificial+intelligence&btnG= [4] links to a bibliography for c++ for artificial intelligence.

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[PDF] researchgate.net MLC++: A machine learning library in C++ R Kohavi, G John, R Long, D Manley… - … Artificial Intelligence …, 1994 - ieeexplore.ieee.org We present MLC++, a library of C++ classes and tools for supervised machine learning. While MLC++ provides general learning algorithms that can be used by end users, the main objective is to provide researchers and experts with a wide variety of tools that can … Cited by 296 Related articles All 13 versions [PDF] jmlr.org libDAI: A free and open source C++ library for discrete approximate inference in graphical models JM Mooij - Journal of Machine Learning Research, 2010 - jmlr.org … In C. Bishop and B. Frey, editors, Proceedings of the Ninth International Workshop on Artificial Intelligence and Statistics (AIS- TATS 2003), 2003. 2172 Page 5. LIBDAI: AFREE AND OPEN SOURCE C++ LIBRARY FOR DISCRETE APPROXIMATE INFERENCE … Cited by 264 Related articles All 15 versions [PDF] stanford.edu Data mining using/spl Mscr//spl Lscr//spl Cscr/++ a machine learning library in C++ R Kohavi, D Sommerfield… - … with Artificial Intelligence, 1996 - ieeexplore.ieee.org Data mining algorithms including machine learning, statistical analysis, and pattern recognition techniques can greatly improve our understanding of data warehouses that are now becoming more widespread. In this paper, we focus on classification algorithms and … Cited by 305 Related articles All 16 versions [PDF] academia.edu Data Mining Using a Machine Learning Library in C++ R Kohavi, D Sommerfield… - … on Artificial Intelligence …, 1997 - World Scientific Data mining algorithms including maching learning, statistical analysis, and pattern recognition techniques can greatly improve our understanding of data warehouses that are now becoming more widespread. In this paper, we focus on classification algorithms and … Cited by 172 Related articles All 12 versions [PDF] docsdrive.com [PDF] Developing an intelligent tutoring system for students learning to program in C++ SSA Naser - Information Technology Journal, Scialert, 2008 - docsdrive.com … Key words: Artificial intelligence, intelligent tutoring system, C++, programming, e-learning INTRODUCTION An Intelligent Tutoring System (ITS) provides individualized computer-based instruction to students (Abu Naser, 2006, 2001 ; Brasilovsky et al, 1996) … Cited by 58 Related articles All 6 versions [PDF] researchgate.net Model-based reasoning for domain modeling in a web-based intelligent tutoring system to help students learn to debug c++ programs AN Kumar - International Conference on Intelligent Tutoring …, 2002 - Springer … associated with storage classes, arrays, structures, loops, nested selection statements, and their applications in C++ … Proceedings of ITS 96 : Third International Conference on Intelligent Tutoring Systems, Montreal, Quebec, June (1996) … Artificial Intelligence, 32 (1987) 97-130 … Cited by 39 Related articles All 13 versions The C++ embeddable rule system DP Miranker, F Burke, J Kolts… - … for Artificial Intelligence …, 1991 - ieeexplore.ieee.org Most rule execution environments, having been derived from LISP, inference on internally defined data types and come packaged with stand-alone development environments. Data derived from outside these systems must be reformatted before they can be evaluated. This … Cited by 32 Related articles All 4 versions Applying the object-oriented paradigm to discrete event simulations using the C++ language DL Eldredge, JD McGregor, MK Summers - Simulation, 1990 - journals.sagepub.com … system. Both of these have evolved from artificial intelligence applications … simulations. It is the purpose of this paper to explore the use of another object-oriented language, C++, for implementing discrete event simulations … Cited by 44 Related articles All 4 versions [PDF] asu.edu [PDF] DEVS–C++ Reference Guide H Cho, Y Cho - The University of Arizona, 1997 - acims.asu.edu Page 1. DEVS-C++ © Reference Guide 31 October 1997 Hyup J. Cho and Young K. Cho Artificial Intelligence and Simulation Research Group Department of Electrical and Computer Engineering The University of Arizona Copyright © The University of Arizona Page 2. - -i … Cited by 24 Related articles [PDF] researchgate.net Columbus-reverse engineering tool and schema for C++ R Ferenc, Á Beszédes, M Tarkiainen… - International …, 2002 - ieeexplore.ieee.org … framework, which has been developed in cooperation between the Re- search Group on Artificial Intelligence in Szeged, the Soft- ware Technology Laboratory of the Nokia Research Center and FrontEndART Ltd. Columbus is able to analyze large C/C++ projects and to extract … Cited by 222 Related articles All 10 versions Related searches

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1 2 3 4 5 6 7 8 9 10 Next HelpPrivacyTerms Ian Martin Ajzenszmidt (talk) 06:02, 18 May 2019 (PDT)

Example code on cpp/chrono

The example code on cpp/chrono contains this line:

std::chrono::duration<double> elapsed_seconds = end-start;

And later:

std::cout << "elapsed time: " << elapsed_seconds.count() << "s\n";

Where is it guaranteed that this overload of std::chrono::duration produces a duration whose resolution will be one tick per second? I can't see such a guarantee here: cpp/chrono/duration/duration.

Therefore I suggest either adding a note to cpp/chrono/duration/duration that the third overload always produces a duration whose resolution is one tick per second or, if there is no such guarantee, editing the example on cpp/chrono to explicitly multiply count with period. — Preceding unsigned comment added by 2a02:a317:2241:7a00:d8b0:a5f3:732e:361f (talk • contribs)

The default template argument for the second template parameter of duration is std::ratio<1>, so std::chrono::duration<double> is std::chrono::duration<double, std::ratio<1>>, which is one tick per second. T. Canens (talk) 13:57, 18 May 2019 (PDT)

Add See also: reference to <iomanip> from std::string?

Just a stray thought for improved navigation. For new C++ users that find themselves at [std::basic_string](https://en.cppreference.com/w/cpp/string/basic_string) and the next place many would need to go a majority of the time would be to <iomanip>. Would it be worth adding a ***See Also:*** reference to <iomanip>. Especially for those who do not yet know <iomanip> exists. Drankinatty (talk) 18:26, 18 May 2019 (PDT)

itoa missing

The C function itoa isn't in the search result, I think it's a missing link or something.

itoa is not a standard C function. See also this. --Fruderica (talk) 06:39, 19 May 2019 (PDT)

Remove the second "the"

In the Exceptions section of https://en.cppreference.com/w/cpp/string/basic_string/to_wstring we have this sentence where "the" is repeated:

"May throw std::bad_alloc from the the std::wstring constructor."

Alexis wilke (talk) 16:14, 20 May 2019 (PDT)