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
You should include the vector header: #include <vector>
Yes, that’s what the standard requires it to be for empty() for any container. ยง 23.2.1 Table 96 of the C++11 standard says: +———-+—————+———————-+ |Expression| Return Type | Operational Semantics| |———-|—————|———————-| |a.empty() |Convertible |a.begin() == a.end() | | |to bool | | | | | | +————————————————-+
You cannot store arrays in a vector or any other container. The type of the elements to be stored in a container (called the container’s value type) must be both copy constructible and assignable. Arrays are neither. You can, however, use an array class template, like the one provided by Boost, TR1, and C++0x: std::vector<std::array<double, … Read more
Yep, the cache in the c++ version takes a hammering. It seems the JIT is better equipped to handle this. If you change the outer for in isUpdateNeeded() to shorter snippets. The difference goes away. The sample below produces a 4x speedup. void isUpdateNeeded() { for (int i = 0; i < numberOfCells; ++i) { … 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
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();
C++20’s std::span If you are able to use C++20, you could use std::span which is a pointer – length pair that gives the user a view into a contiguous sequence of elements. It is some sort of a std::string_view, and while both std::span and std::string_view are non-owning views, std::string_view is a read-only view. From the … Read more
You can use std::find as follows: if (std::find(v.begin(), v.end(), “abc”) != v.end()) { // Element in vector. } To be able to use std::find: include <algorithm>.
From C++11 onwards, you should prefer: #include <algorithm> #include <random> auto rng = std::default_random_engine {}; std::shuffle(std::begin(cards_), std::end(cards_), rng); Live example on Coliru Make sure to reuse the same instance of rng throughout multiple calls to std::shuffle if you intend to generate different permutations every time! Moreover, if you want your program to create different sequences … Read more