Mfcttrf

Why isn't "I've" a proper response?

what mathematical functions can we use to generate patterns for rhythm (meter and notes)?

How to prevent clipped screen edges on my TV, HDMI-connected?

The Knight's estate

What is the difference between computational complexity and time complexity?

Why do banks “park” their money at the European Central Bank?

Is for(( ... )) ... ; a valid shell syntax? In which shells?

Is it possible to perform a regression where you have an unknown / unknowable feature variable?

Why did MS-DOS applications built using Turbo Pascal fail to start with a division by zero error on faster systems?

How to find out the average duration of the peer-review process for a given journal?

Does norwegian.no airline overbook flights?

Pythagorean triple with hypotenuse a power of 2

Is gzip atomic?

Why did this happen to Thanos's ships at the end of "Avengers: Endgame"?

Avoiding racist tropes in fantasy

Nothing like a good ol' game of ModTen

“T” in subscript in formulas

What to say to a student who has failed?

Would it be possible to have a GMO that produces chocolate?

Non-visual Computers - thoughts?

Is "The life is beautiful" incorrect or just very non-idiomatic?

Can you pop_back a vector and still use the iterator to the last element?

Is there any method of inflicting the incapacitated condition and no other condition?

Why is my Earth simulation slower than the reality?

Can you pop_back a vector and still use the iterator to the last element?

How do I erase an element from std::vector<> by index?Test if a vector contains a given elementWhat is the most effective way to get the index of an iterator of an std::vector?What is the easiest way to initialize a std::vector with hardcoded elements?std::vector iterator invalidationVector iterator comparisonusing erase with remove_ifC++ vector content not changed while using iterator

.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty margin-bottom:0;

7

1

I wonder what happens if I have an iterator on the last element of the vector and do pop_back.

std::set<int> s;
s.insert(5);

std::vector<int> v = 1, 2, 3, 4, 5;

for (auto it = v.begin(); it != v.end();) 
 if (s.count(*it)) 
 std::swap(*it, v.back());
 v.pop_back();
 else 
 ++it;
 

Code above works properly (v is 1, 2, 3, 4 after that block) at least with clang, but is it correct to check if it == v.end() if it is invalidated?

c++ vector iterator

share|improve this question

edited 7 hours ago

Nicol Bolas

305k3737 gold badges511511 silver badges691691 bronze badges

asked 8 hours ago

user3365922user3365922

5855 bronze badges

New contributor

user3365922 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

add a comment | 

7

1

I wonder what happens if I have an iterator on the last element of the vector and do pop_back.

std::set<int> s;
s.insert(5);

std::vector<int> v = 1, 2, 3, 4, 5;

for (auto it = v.begin(); it != v.end();) 
 if (s.count(*it)) 
 std::swap(*it, v.back());
 v.pop_back();
 else 
 ++it;
 

Code above works properly (v is 1, 2, 3, 4 after that block) at least with clang, but is it correct to check if it == v.end() if it is invalidated?

c++ vector iterator

share|improve this question

edited 7 hours ago

Nicol Bolas

305k3737 gold badges511511 silver badges691691 bronze badges

asked 8 hours ago

user3365922user3365922

5855 bronze badges

New contributor

user3365922 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

add a comment | 

I wonder what happens if I have an iterator on the last element of the vector and do pop_back.

std::set<int> s;
s.insert(5);

std::vector<int> v = 1, 2, 3, 4, 5;

for (auto it = v.begin(); it != v.end();) 
 if (s.count(*it)) 
 std::swap(*it, v.back());
 v.pop_back();
 else 
 ++it;
 

Code above works properly (v is 1, 2, 3, 4 after that block) at least with clang, but is it correct to check if it == v.end() if it is invalidated?

c++ vector iterator

share|improve this question

edited 7 hours ago

Nicol Bolas

305k3737 gold badges511511 silver badges691691 bronze badges

asked 8 hours ago

user3365922user3365922

5855 bronze badges

New contributor

user3365922 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

std::set<int> s;
s.insert(5);

std::vector<int> v = 1, 2, 3, 4, 5;

for (auto it = v.begin(); it != v.end();) 
 if (s.count(*it)) 
 std::swap(*it, v.back());
 v.pop_back();
 else 
 ++it;
 

share|improve this question

edited 7 hours ago

Nicol Bolas

305k3737 gold badges511511 silver badges691691 bronze badges

asked 8 hours ago

user3365922user3365922

5855 bronze badges

New contributor

user3365922 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

share|improve this question

edited 7 hours ago

Nicol Bolas

305k3737 gold badges511511 silver badges691691 bronze badges

asked 8 hours ago

user3365922user3365922

5855 bronze badges

New contributor

user3365922 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

edited 7 hours ago

Nicol Bolas

305k3737 gold badges511511 silver badges691691 bronze badges

edited 7 hours ago

Nicol Bolas

305k3737 gold badges511511 silver badges691691 bronze badges

asked 8 hours ago

user3365922user3365922

5855 bronze badges

New contributor

user3365922 is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.

asked 8 hours ago

user3365922user3365922

5855 bronze badges

1 Answer
1

active

oldest

votes

8

Your instincts are good; vector::pop_back invalidates iterators and references to the last element. If it is such an iterator, then it will be invalidated, and thus cannot be compared with v.end().

It would be much better to fix this by using algorithms and the erase-remove idiom:

auto last_it = std::remove_if(v.begin(), v.end(), [&](const auto &val) return s.count(val) != 0;);
v.erase(last_it, v.end());

share|improve this answer

answered 7 hours ago

Nicol BolasNicol Bolas

305k3737 gold badges511511 silver badges691691 bronze badges

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
);



);

user3365922 is a new contributor. Be nice, and check out our Code of Conduct.

draft saved

draft discarded

Sign up or log in

StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);

Sign up using Google

Sign up using Facebook

Sign up using Email and Password

Post as a guest

Name

Email

Required, but never shown

StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f57629086%2fcan-you-pop-back-a-vector-and-still-use-the-iterator-to-the-last-element%23new-answer', 'question_page');

);

Post as a guest

Name

Email

Required, but never shown

8

Your instincts are good; vector::pop_back invalidates iterators and references to the last element. If it is such an iterator, then it will be invalidated, and thus cannot be compared with v.end().

It would be much better to fix this by using algorithms and the erase-remove idiom:

auto last_it = std::remove_if(v.begin(), v.end(), [&](const auto &val) return s.count(val) != 0;);
v.erase(last_it, v.end());

share|improve this answer

answered 7 hours ago

Nicol BolasNicol Bolas

305k3737 gold badges511511 silver badges691691 bronze badges

add a comment | 

8

Your instincts are good; vector::pop_back invalidates iterators and references to the last element. If it is such an iterator, then it will be invalidated, and thus cannot be compared with v.end().

It would be much better to fix this by using algorithms and the erase-remove idiom:

auto last_it = std::remove_if(v.begin(), v.end(), [&](const auto &val) return s.count(val) != 0;);
v.erase(last_it, v.end());

share|improve this answer

answered 7 hours ago

Nicol BolasNicol Bolas

305k3737 gold badges511511 silver badges691691 bronze badges

add a comment | 

Your instincts are good; vector::pop_back invalidates iterators and references to the last element. If it is such an iterator, then it will be invalidated, and thus cannot be compared with v.end().

It would be much better to fix this by using algorithms and the erase-remove idiom:

auto last_it = std::remove_if(v.begin(), v.end(), [&](const auto &val) return s.count(val) != 0;);
v.erase(last_it, v.end());

share|improve this answer

answered 7 hours ago

Nicol BolasNicol Bolas

305k3737 gold badges511511 silver badges691691 bronze badges

auto last_it = std::remove_if(v.begin(), v.end(), [&](const auto &val) return s.count(val) != 0;);
v.erase(last_it, v.end());

share|improve this answer

answered 7 hours ago

Nicol BolasNicol Bolas

305k3737 gold badges511511 silver badges691691 bronze badges

answered 7 hours ago

Nicol BolasNicol Bolas

305k3737 gold badges511511 silver badges691691 bronze badges

answered 7 hours ago

Nicol BolasNicol Bolas

305k3737 gold badges511511 silver badges691691 bronze badges