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This question is made while I answer this another question.
N3337 23.3.6.3 "vector capacity" says (it's in 770 page):
void resize(size_type sz);
Effects: If
sz <= size(), equivalent toerase(begin() + sz, end());. Ifsize() < sz, appendssz - size()value-initialized elements to the sequence.Requires: T shall be CopyInsertable into *this.
However, clang++ says it's okay though T is not copyable. And I think it makes sense that resize(size_type) requires only destroyable/moveable/default constructable. It destroys if sz <= size, appends (which uses default constructing, and destroying and moving if the capacity is not enough) if size() < sz.
What is truth? Is it a standard defect? Or is it a mistake of both clang++ and me?
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The C++ function std::vector::resize() changes the size of vector. If n is smaller than current size then extra elements are destroyed. If n is greater than current container size then new elements are inserted at the end of vector. If val is specified then new elements are initialed with val.
std::vector::resizeResizes the container to contain count elements. If the current size is greater than count , the container is reduced to its first count elements as if by repeatedly calling pop_back() . If the current size is less than count , additional elements are appended and initialized with copies of value .
Resizing a vector doesn't destroy the values stored in the vector (except for those beyond the new size when shrinking, of course), however growing a vector beyond its capacity will copy (or, in C++11, move) them to a new place, thus invalidating and iterators, pointers or references to those elements.
As mentioned above, std::vector is a templated class that represents dynamic arrays. std::vector typically allocates memory on the heap (unless you override this behavior with your own allocator). The std::vector class abstracts memory management, as it grows and shrinks automatically if elements are added or removed.
You are correct. It was a defect in C++11 that was fixed for C++14 by http://cplusplus.github.io/LWG/lwg-defects.html#2033
The current wording says:
Effects: If
sz < size(), erases the lastsize() - szelements from the sequence. Otherwise, appendssz - size()default-inserted elements to the sequence.Requires:
Tshall beMoveInsertableandDefaultInsertableinto*this.
The requirement on Destructible is in Table 95 and applies to all operations on all containers, not just resize().
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