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I'm writing a parallel implementation of some data structures. I'd like to find out if someone know about difference in performance between pure pointers and std::vector. If you know trustful docs about it, please write URL/book name/whatever. Any hints are welcome!

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    What is the commonality between pointers and std::vector? Commented Nov 25, 2010 at 21:14
  • Unfortunately I know nothing about this, but +1 for a very good, probably very common question :-) Commented Nov 25, 2010 at 21:15
  • Both can store any kind of data. I ask cause I don't know which one is faster. Commented Nov 25, 2010 at 21:15
  • I assume that by "pure pointers" you mean hand-crafted dynamically allocated arrays? Commented Nov 25, 2010 at 21:17
  • @Adam: no, they can't hold "any kind of data". The can hold n>=0 objects of the same type. What do you mean exactly? Commented Nov 25, 2010 at 21:18

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The difference is usage and implementation relative.

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+1: std::vector<> is just a friendly dynamically allocated array.
I "hid" the developpement of this answer in "history", but the initial sentence should be enough for most of us.
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You can make std::vector as fast as normal pointers by using the unchecked operator[] and resizing appropriately. The reality is that vector is a compile-time abstraction over a pointer- not a runtime one, unless you choose to use extras. What's much more important is the vastly increased safety vector offers- debugging iterators, automatic and safe resource management, etc. There is no reason to use a raw pointer.

Edit: My reference is that profiling run you did before you even considered losing the safety of vector.

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According to this answer in a similar question, accessing an element in a dynamically-allocated array versus a std::vector will be roughly the same. There's some good analysis in that question and in this one as well.

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If you mean to compare a std::vector with some hand-written dynamic array here are some points of reference:

  • The resizing factor on insertion is important. This factor isn't specified by the standard but is usually between 1.5 or 2 and it must guarantee amortized constant time on insertion operations.
  • The allocator: A lot of the performance depends on the allocation mechanism that is used, same goes for your pointers.
  • Boundary checking can occur in std::vector if you call vector::at which cannot happen with raw pointers.
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the resizing factor isn't relevant if you're making an apples to apples comparison. A raw array has to be sized up front, so presumably you'd do the same with vector.
@jalf: it's not really clear what "pure pointers" means, so it's more of an apples to some-unspecified-fruit-in-a-locked-box comparison.
@jalf: I thought if he compared something with vector dynamic resizing is a must. If he doesn't need dynamic resizing he should use std::array anyway.

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