The current std::vector doesn’t provide any capability or interface to take ownership of previously allocated storage. Presumably it would be too easy to pass a stack address in by accident, allowing more problems than it solved. If you want to avoid copying into a vector, you’ll either need to use vectors through your entire call … Read more
You use a move_iterator with insert: v1.insert(v1.end(), make_move_iterator(v2.begin()), make_move_iterator(v2.end())); The example in 24.5.3 is almost exactly this. You’ll get the optimization you want if (a) vector::insert uses iterator-tag dispatch to detect the random-access iterator and precalculate the size (which you’ve assumed it does in your example that copies), and (b) move_iterator preserves the iterator category … Read more
So what are the benefits and the usage of std::dynarray, when we can use std::vector which is more dynamic (Re-sizable)? dynarray is smaller and simpler than vector, because it doesn’t need to manage separate size and capacity values, and it doesn’t need to store an allocator. However the main performance benefit is intended to come … Read more
Adding elements to a vector There are several ways to add data to a vector: create an empty vector, push_back() elements into it. create an empty vector, allocate some capacity with reserve(), then push_back() elements into it. create a vector of n elements, use indexing and copy-assignment. create an empty vector, emplace_back() elements into it. … Read more
Calling resize() with a smaller size has no effect on the capacity of a vector. It will not free memory. The standard idiom for freeing memory from a vector is to swap() it with an empty temporary vector: std::vector<T>().swap(vec);. If you want to resize downwards you’d need to copy from your original vector into a … Read more
You can get a pointer to the first element as follows: int* pv = &v[0]; This pointer is only valid as long as the vector is not reallocated. Reallocation happens automatically if you insert more elements than will fit in the vector’s remaining capacity (that is, if v.size() + NumberOfNewElements > v.capacity(). You can use … Read more
Your code (vector1 == vector2) is correct C++ syntax. There is an == operator for vectors. If you want to compare short vector with a portion of a longer vector, you can use theequal() operator for vectors. (documentation here) Here’s an example: using namespace std; if( equal(vector1.begin(), vector1.end(), vector2.begin()) ) DoSomething();
You have no right to get a segmentation fault. For that matter, a segmentation fault isn’t even part of C++. Your program is removing all elements from the vector, and you’re illegally accessing the container out of bounds. This is undefined behaviour, which means anything can happen. And indeed, something happened.
23.2.1 / p10 / b6: Unless otherwise specified … no swap() function invalidates any references, pointers, or iterators referring to the elements of the containers being swapped. … Nowhere does it “specify otherwise” for vector. So this outlaws the SBO for vector. string is not bound by this rule because it does “specify otherwise” in … Read more
What happens: x is inserted via push_back. One copy occurs: The newly created element is initialized with the argument. my_int is taken over as zero because xs default constructor initialized it so. The second element is push_back‘d; The vector needs to reallocate the memory since the internal capacity was reached. As no move constructor is … Read more