stdarray

问题 I want to create an object of std::array<T, N> but the problem is I can only use functions that return a constexpr type or compiler will complain. The problem here is that I need to calculate the length of this array based on another array's size which could be something like this: template <typename T> struct DataLength { template <typename iter> size_t maxPossibleLength(iter begin, iter end) { size_t m_size = 0; while (begin != end) { m_size = m_size << 8 | std::numeric_limits<T>::max(); /*

问题 Given that std::array<T,N>::size is constexpr, in the snippet below Why does it matter that Foo1::u is not a static member? The type is known at compile time and so is its size() . What's wrong with Foo2::bigger() ? Listing: // x86-64 gcc 10.1 // -O3 --std=c++20 -pedantic -Wall -Werror #include <array> #include <cstdint> union MyUnion { std::array<uint8_t,32> bytes; std::array<uint32_t,8> words; }; struct Foo1 { MyUnion u; static constexpr size_t length {u.bytes.size()}; //invalid use of non

问题 I want to use a 2d std::array as I've to use bound check at certain point in my program. For 1d array, I would do this: #include <iostream> #include <array> int main (){ std::array<int,4> myarray; for (int i=0; i<10; i++){ myarray.at(i) = i+1; } } How do I do it for a 2d array. Can I make use of auto in it? 回答1: std::array is 1-dimensional, there is no such thing as a 2-dimensional std::array . You would simply have to use an inner std::array as the element type of an outer std::array , eg:

问题 I have a code in which at the end of a function I need to cast from int to double all the elements of an array in order to being able to do a final push_back before exiting the function. The code I have right now is: template <class T, size_t dims> class A { typedef typename std::array<int, dims> ArrayInt; typedef typename std::array<double, dims> ArrayDouble; typedef typename std::vector <ArrayDouble> VectorDouble; /* ...*/ foo() { /* ...*/ ArrayInt myArrayInt; ArrayDouble myArrayDouble;

来源： https://stackoverflow.com/questions/63821007/how-can-i-construct-an-stdarray-filled-with-some-uniform-value

来源： https://stackoverflow.com/questions/63821007/how-can-i-construct-an-stdarray-filled-with-some-uniform-value

来源： https://stackoverflow.com/questions/60235741/in-c-what-is-the-point-of-stdarray-if-the-size-has-to-be-determined-at-compi

来源： https://stackoverflow.com/questions/60235741/in-c-what-is-the-point-of-stdarray-if-the-size-has-to-be-determined-at-compi

问题 can anybody explaine the memory layout of std::vector<std::array<int, 5>> vec(2) does it provide contiguous memory block of a 2D array with 2 rows of 5 elements? To my understanding, the vector of vectors std::vector<std::vector<int>> vec(2, std::vector<int>(5)) provide the memory layout of two contiguous arrays of length 5 element s in different locations in memory. Will it be the same for the vector of arrays? 回答1: Arrays do not have any indirection, but just store their data "directly".

问题 If I want to build a very simple array like int myArray[3] = {1,2,3}; Should I use std::array instead ? std::array<int, 3> a = {{1, 2, 3}}; What are the advantages of using std::array over usual ones? Is it more performant ? Just easier to handle for copy/access ? 回答1: What are the advantages of using std::array over usual ones? It has friendly value semantics, so that it can be passed to or returned from functions by value. Its interface makes it more convenient to find the size, and use