c++ - Why set the size of a vector -


is there performance reason why vector initialized size?

for example vector<myclass> v(10); opposed vector<myclass> v , push_back needed?

vector<myclass> v(10) pre-allocates internal array once time , auto-fills 10 default-constructed myclass objects.

vector<myclass> v not pre-allocate array, can use reserve() , resize() that.

push_back() re-allocate , copy internal array each time new size() exceed current capacity().


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