Return element at index in a vector

Question

How can I remove an element at a specified index in a vector, and then return that element? Is there a method for that?

Does it have to be in that order? You can use `operator[]` or `at()`, followed by `erase()` if not. — chris, Nov 21 '12 at 19:08
Duplicate? http://stackoverflow.com/questions/39912/how-do-i-remove-an-item-from-a-stl-vector-with-a-certain-value — Roman Byshko, Nov 21 '12 at 19:08
@Beginner, Not really. It isn't searching by value, so using `remove` is a bit pointless. — chris, Nov 21 '12 at 19:09

score 5 · Accepted Answer · edited Nov 22 '12 at 23:14

5

erase can remove an element at a specified index, but does not return that element.

You can just do:

aboutToBeErased = myVector.at(index);
myVector.erase(myVector.begin() + index);

Be careful though, vectors are not good at removing elements that aren't at the end of the vector. This can be a costly operation for large vectors.

edited Nov 22 '12 at 23:14

answered Nov 21 '12 at 19:10

llakais

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`vector:erase` doesn't take an `int` as argument – default Nov 21 '12 at 19:13
for the erase line, I got error "IntelliSense: too few arguments in function call" – Chin Nov 21 '12 at 19:13
should be `myVector.erase(std::next(myVector.begin(), index));` – David Nov 21 '12 at 19:14

Anirudh Ramanathan · Answer 2 · 2012-11-21T19:25:45.490

3

To get the element, you can use std::vector::at()
```
value = mVector.at(n);
```
To erase, std::vector::erase() The following would erase item no. n+1 and resize your vector.
```
mVector.erase (mVector.begin()+n);
```

Erase shifts all elements and hence, indexes if you do erase an element in the middle.

edited Nov 21 '12 at 19:25

answered Nov 21 '12 at 19:09

Anirudh Ramanathan

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The asker wants the element too. – Joseph Mansfield Nov 21 '12 at 19:10

Yakk - Adam Nevraumont · Answer 3 · 2012-11-21T22:25:13.057

2

Here is a function, written in C++11, that will get the nth element from a vector and erase it reasonably efficiently:

template<typename Vector>
typename Vector::value_type getAndErase( Vector& vec, size_t index )
{
  Assert( index < vec.size() );
  typename Vector::value_type retval = std::move(vec[index]);
  vec.erase( vec.begin()+index );
  return retval;
}

edited Nov 21 '12 at 22:25

answered Nov 21 '12 at 19:16

Yakk - Adam Nevraumont

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Return element at index in a vector

3 Answers3