What's the difference between `auto x = vector()` and `vector x`? Announcing the arrival of Valued Associate #679: Cesar Manara Planned maintenance scheduled April 17/18, 2019 at 00:00UTC (8:00pm US/Eastern) The Ask Question Wizard is Live! Data science time! April 2019 and salary with experience Should we burninate the [wrap] tag?What is the difference between #include <filename> and #include “filename”?Regular cast vs. static_cast vs. dynamic_castWhat are the differences between a pointer variable and a reference variable in C++?The Definitive C++ Book Guide and ListDifference between private, public, and protected inheritanceWhat is the difference between const int*, const int * const, and int const *?Why is “using namespace std” considered bad practice?Why are elementwise additions much faster in separate loops than in a combined loop?What is the difference between 'typedef' and 'using' in C++11?Why is it faster to process a sorted array than an unsorted array?
Gastric acid as a weapon
Is 1 ppb equal to 1 μg/kg?
Withdrew £2800, but only £2000 shows as withdrawn on online banking; what are my obligations?
Antler Helmet: Can it work?
What is a Meta algorithm?
Super Attribute Position on Product Page Magento 1
Why are there no cargo aircraft with "flying wing" design?
Why is "Captain Marvel" translated as male in Portugal?
Should I discuss the type of campaign with my players?
Is above average number of years spent on PhD considered a red flag in future academia or industry positions?
Is the address of a local variable a constexpr?
Did Kevin spill real chili?
What LEGO pieces have "real-world" functionality?
What would be the ideal power source for a cybernetic eye?
Why is black pepper both grey and black?
What are 'alternative tunings' of a guitar and why would you use them? Doesn't it make it more difficult to play?
Disable hyphenation for an entire paragraph
What is this single-engine low-wing propeller plane?
Check which numbers satisfy the condition [A*B*C = A! + B! + C!]
How can I fade player when goes inside or outside of the area?
What is the correct way to use the pinch test for dehydration?
Is the Standard Deduction better than Itemized when both are the same amount?
What causes the vertical darker bands in my photo?
do i need a schengen visa for a direct flight to amsterdam?
What's the difference between `auto x = vector()` and `vector x`?
Announcing the arrival of Valued Associate #679: Cesar Manara
Planned maintenance scheduled April 17/18, 2019 at 00:00UTC (8:00pm US/Eastern)
The Ask Question Wizard is Live!
Data science time! April 2019 and salary with experience
Should we burninate the [wrap] tag?What is the difference between #include <filename> and #include “filename”?Regular cast vs. static_cast vs. dynamic_castWhat are the differences between a pointer variable and a reference variable in C++?The Definitive C++ Book Guide and ListDifference between private, public, and protected inheritanceWhat is the difference between const int*, const int * const, and int const *?Why is “using namespace std” considered bad practice?Why are elementwise additions much faster in separate loops than in a combined loop?What is the difference between 'typedef' and 'using' in C++11?Why is it faster to process a sorted array than an unsorted array?
.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty height:90px;width:728px;box-sizing:border-box;
I am writing some code and have a question.
What is the difference between auto x = vector<int>(); and vector<int> x;? Are they all the same or there's some difference with the complexity?
c++ vector stl initialization
edited 1 hour ago
songyuanyao
94.5k11182250
asked 1 hour ago
AutoratchAutoratch
555
add a comment |
I am writing some code and have a question.
What is the difference between auto x = vector<int>(); and vector<int> x;? Are they all the same or there's some difference with the complexity?
c++ vector stl initialization
edited 1 hour ago
songyuanyao
94.5k11182250
asked 1 hour ago
AutoratchAutoratch
555
2
The first results in a call to a default constructor and a call to a move constructor. The second results in a call to a default constructor. Even if the compiler optimizes both to result in the same assembly, the second one is the one to go for readability.
– DeiDei
1 hour ago
add a comment |
I am writing some code and have a question.
What is the difference between auto x = vector<int>(); and vector<int> x;? Are they all the same or there's some difference with the complexity?
c++ vector stl initialization
edited 1 hour ago
songyuanyao
94.5k11182250
asked 1 hour ago
AutoratchAutoratch
555
I am writing some code and have a question.
What is the difference between auto x = vector<int>(); and vector<int> x;? Are they all the same or there's some difference with the complexity?
c++ vector stl initialization
c++ vector stl initialization
edited 1 hour ago
songyuanyao
94.5k11182250
asked 1 hour ago
AutoratchAutoratch
555
edited 1 hour ago
songyuanyao
94.5k11182250
asked 1 hour ago
AutoratchAutoratch
555
edited 1 hour ago
songyuanyao
94.5k11182250
edited 1 hour ago
songyuanyao
94.5k11182250
edited 1 hour ago
songyuanyao
94.5k11182250
94.5k11182250
asked 1 hour ago
AutoratchAutoratch
555
asked 1 hour ago
AutoratchAutoratch
555
asked 1 hour ago
AutoratchAutoratch
555
555
2
The first results in a call to a default constructor and a call to a move constructor. The second results in a call to a default constructor. Even if the compiler optimizes both to result in the same assembly, the second one is the one to go for readability.
– DeiDei
1 hour ago
add a comment |
2
The first results in a call to a default constructor and a call to a move constructor. The second results in a call to a default constructor. Even if the compiler optimizes both to result in the same assembly, the second one is the one to go for readability.
– DeiDei
1 hour ago
2
2
The first results in a call to a default constructor and a call to a move constructor. The second results in a call to a default constructor. Even if the compiler optimizes both to result in the same assembly, the second one is the one to go for readability.
– DeiDei
1 hour ago
The first results in a call to a default constructor and a call to a move constructor. The second results in a call to a default constructor. Even if the compiler optimizes both to result in the same assembly, the second one is the one to go for readability.
– DeiDei
1 hour ago
add a comment |
1 Answer
1
active
oldest
votes
They have the same effect since C++17. Both construct an object named x with type std::vector<int>, which is initialized by the default constructor of std::vector.
Precisely the 1st one is copy initialization, x is copy-initialized from a value-initialized temporary. From C++17 this kind of copy elision is guaranteed, as the result x is initialized by the default constructor of std::vector directly. Before C++17, copy elision is an optimization:
even when it takes place and the copy/move (since C++11) constructor is not called, it still must be present and accessible (as if no optimization happened at all), otherwise the program is ill-formed:
The 2nd one is default initialization, as a class type x is initialized by the default constructor of std::vector.
answered 1 hour ago
songyuanyaosongyuanyao
94.5k11182250
add a comment |
Your Answer
StackExchange.ifUsing("editor", function ()
StackExchange.using("externalEditor", function ()
StackExchange.using("snippets", function ()
StackExchange.snippets.init();
);
);
, "code-snippets");
StackExchange.ready(function()
var channelOptions =
tags: "".split(" "),
id: "1"
;
initTagRenderer("".split(" "), "".split(" "), channelOptions);
StackExchange.using("externalEditor", function()
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled)
StackExchange.using("snippets", function()
createEditor();
);
else
createEditor();
);
function createEditor()
StackExchange.prepareEditor(
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader:
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
,
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
);
);
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
var $window = $(window),
onScroll = function(e)
var $elem = $('.new-login-left'),
docViewTop = $window.scrollTop(),
docViewBottom = docViewTop + $window.height(),
elemTop = $elem.offset().top,
elemBottom = elemTop + $elem.height();
if ((docViewTop elemBottom))
StackExchange.using('gps', function() StackExchange.gps.track('embedded_signup_form.view', location: 'question_page' ); );
$window.unbind('scroll', onScroll);
;
$window.on('scroll', onScroll);
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f55700049%2fwhats-the-difference-between-auto-x-vectorint-and-vectorint-x%23new-answer', 'question_page');
);
Post as a guest
Required, but never shown
1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
They have the same effect since C++17. Both construct an object named x with type std::vector<int>, which is initialized by the default constructor of std::vector.
Precisely the 1st one is copy initialization, x is copy-initialized from a value-initialized temporary. From C++17 this kind of copy elision is guaranteed, as the result x is initialized by the default constructor of std::vector directly. Before C++17, copy elision is an optimization:
even when it takes place and the copy/move (since C++11) constructor is not called, it still must be present and accessible (as if no optimization happened at all), otherwise the program is ill-formed:
The 2nd one is default initialization, as a class type x is initialized by the default constructor of std::vector.
answered 1 hour ago
songyuanyaosongyuanyao
94.5k11182250
add a comment |
They have the same effect since C++17. Both construct an object named x with type std::vector<int>, which is initialized by the default constructor of std::vector.
Precisely the 1st one is copy initialization, x is copy-initialized from a value-initialized temporary. From C++17 this kind of copy elision is guaranteed, as the result x is initialized by the default constructor of std::vector directly. Before C++17, copy elision is an optimization:
even when it takes place and the copy/move (since C++11) constructor is not called, it still must be present and accessible (as if no optimization happened at all), otherwise the program is ill-formed:
The 2nd one is default initialization, as a class type x is initialized by the default constructor of std::vector.
answered 1 hour ago
songyuanyaosongyuanyao
94.5k11182250
add a comment |
They have the same effect since C++17. Both construct an object named x with type std::vector<int>, which is initialized by the default constructor of std::vector.
Precisely the 1st one is copy initialization, x is copy-initialized from a value-initialized temporary. From C++17 this kind of copy elision is guaranteed, as the result x is initialized by the default constructor of std::vector directly. Before C++17, copy elision is an optimization:
even when it takes place and the copy/move (since C++11) constructor is not called, it still must be present and accessible (as if no optimization happened at all), otherwise the program is ill-formed:
The 2nd one is default initialization, as a class type x is initialized by the default constructor of std::vector.
answered 1 hour ago
songyuanyaosongyuanyao
94.5k11182250
They have the same effect since C++17. Both construct an object named x with type std::vector<int>, which is initialized by the default constructor of std::vector.
Precisely the 1st one is copy initialization, x is copy-initialized from a value-initialized temporary. From C++17 this kind of copy elision is guaranteed, as the result x is initialized by the default constructor of std::vector directly. Before C++17, copy elision is an optimization:
even when it takes place and the copy/move (since C++11) constructor is not called, it still must be present and accessible (as if no optimization happened at all), otherwise the program is ill-formed:
The 2nd one is default initialization, as a class type x is initialized by the default constructor of std::vector.
answered 1 hour ago
songyuanyaosongyuanyao
94.5k11182250
edited 1 hour ago
answered 1 hour ago
songyuanyaosongyuanyao
94.5k11182250
answered 1 hour ago
songyuanyaosongyuanyao
94.5k11182250
answered 1 hour ago
songyuanyaosongyuanyao
94.5k11182250
94.5k11182250
add a comment |
add a comment |
Thanks for contributing an answer to Stack Overflow!
- Please be sure to answer the question. Provide details and share your research!
But avoid …
- Asking for help, clarification, or responding to other answers.
- Making statements based on opinion; back them up with references or personal experience.
To learn more, see our tips on writing great answers.
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
var $window = $(window),
onScroll = function(e)
var $elem = $('.new-login-left'),
docViewTop = $window.scrollTop(),
docViewBottom = docViewTop + $window.height(),
elemTop = $elem.offset().top,
elemBottom = elemTop + $elem.height();
if ((docViewTop elemBottom))
StackExchange.using('gps', function() StackExchange.gps.track('embedded_signup_form.view', location: 'question_page' ); );
$window.unbind('scroll', onScroll);
;
$window.on('scroll', onScroll);
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f55700049%2fwhats-the-difference-between-auto-x-vectorint-and-vectorint-x%23new-answer', 'question_page');
);
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
var $window = $(window),
onScroll = function(e)
var $elem = $('.new-login-left'),
docViewTop = $window.scrollTop(),
docViewBottom = docViewTop + $window.height(),
elemTop = $elem.offset().top,
elemBottom = elemTop + $elem.height();
if ((docViewTop elemBottom))
StackExchange.using('gps', function() StackExchange.gps.track('embedded_signup_form.view', location: 'question_page' ); );
$window.unbind('scroll', onScroll);
;
$window.on('scroll', onScroll);
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
var $window = $(window),
onScroll = function(e)
var $elem = $('.new-login-left'),
docViewTop = $window.scrollTop(),
docViewBottom = docViewTop + $window.height(),
elemTop = $elem.offset().top,
elemBottom = elemTop + $elem.height();
if ((docViewTop elemBottom))
StackExchange.using('gps', function() StackExchange.gps.track('embedded_signup_form.view', location: 'question_page' ); );
$window.unbind('scroll', onScroll);
;
$window.on('scroll', onScroll);
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Sign up or log in
StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
var $window = $(window),
onScroll = function(e)
var $elem = $('.new-login-left'),
docViewTop = $window.scrollTop(),
docViewBottom = docViewTop + $window.height(),
elemTop = $elem.offset().top,
elemBottom = elemTop + $elem.height();
if ((docViewTop elemBottom))
StackExchange.using('gps', function() StackExchange.gps.track('embedded_signup_form.view', location: 'question_page' ); );
$window.unbind('scroll', onScroll);
;
$window.on('scroll', onScroll);
);
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Sign up using Google
Sign up using Facebook
Sign up using Email and Password
Post as a guest
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
Required, but never shown
2
The first results in a call to a default constructor and a call to a move constructor. The second results in a call to a default constructor. Even if the compiler optimizes both to result in the same assembly, the second one is the one to go for readability.
– DeiDei
1 hour ago