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I have two vectors:
std::vector<int> v1, v2; // Filling v1 ... And now I need to copy v1 to v2. Is there any reason to prefer
v2 = v1;
to
std::copy (v1.begin(), v1.end(), v2.begin());
(or vice versa)?
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The standard algorithm for copying is std::copy . We can use it for copying elements from the source vector to the destination vector.
Vector has an inbuilt function too to copy contents from other content. It's named assign() function. It's again a deep copy method.
Complexity :- O(n) as copy() takes linear time to traverse elements. But begin(),end() and back_inserter() takes constant time. This function takes 2 arguments, first iterator to old vector and last iterator to old vector. It then assigns values of old vector to new vector.
As a rule of thumb, you should use: a std::array if the size in fixed at compile time. a std::vector is the size is not fixed at compile time. a pointer on the address of their first element is you need low level access.
Generally I would strongly prefer v2 = v1:
std::copy won't work if v2 doesn't have the same length as v1 (it won't resize it, so it will retain some of the old elements best case (v2.size() > v1.size() and overwrite some random data used elsewhere in the program worst casev1 is about to expire (and you use C++11) you can easily modify it to move the contentsstd::copy, since the implementers would probably use std::copy internally, if it gave a performance benefit.In conclusion, std::copy is less expressive, might do the wrong thing and isn't even faster. So there isn't really any reason to use it here.
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