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Programming Talk / C++ / C# - std::vector erase or swap + pop back?

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heyufool1
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Posted: 11th Jan 2013 03:57 Edited at: 11th Jan 2013 03:57
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Hello! I'm working on a C++ game and I have a small question regarding removing data from a vector. I'm currently using this method:


However, the same thing can be accomplished doing this:


My question is, which way is better (Specifically speed)? In this case the order of the vector doesn't matter so that's not a concern. Thanks for any input!

- Demo!
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WLGfx
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Posted: 11th Jan 2013 13:51
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Yep, you can erase more than one: http://www.cplusplus.com/reference/vector/vector/erase/

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Dar13
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Posted: 12th Jan 2013 04:39 Edited at: 12th Jan 2013 04:40
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What's wrong with
?

EDIT: Or maybe you want to extract the data from the vector before you clear it? I'm not really sure what you want to do here.

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Jeff032
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Posted: 12th Jan 2013 05:06
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erase() has a linear complexity (time increases linearly with the number of elements), since it shifts all the elements after the one that was deleted.

swap() and pop_back() both have a constant complexity (same amount of time regardless of the number of elements).

So theoretically, you would be better off with swap() and pop_back(), but you might not see much of a difference for smaller vectors.
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heyufool1
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Posted: 12th Jan 2013 06:34 Edited at: 12th Jan 2013 06:34
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@WLGfx - I'm referring to the speed of the two methods.
@Dar13 - I only wanted to erase one item, not the whole vector.
@Jeff032 - Thanks for the information! Definitely makes sense now that the swap() and pop_back() would be slightly faster

- Demo!
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