基于多维std :: array的范围

Question

Tried looking around for this but only found examples using built in array not std::array obj.

// array arr of size 5
array< array<int, 10>, 10> arr = { 0 };

srand((unsigned)time(0));

// initialize elements
for ()
{
    for()
    {
        item = rand() % 100 + 1;
    }
}

basic example trying to initialize 2D array obj to random values. im not sure what to put between the () of the for loops

Answer 1

auto& comes in handy here. Well, the first range-for loop will take on references to each array in the array. the second takes on references to each element in the innermost array. Like:

// initialize elements
for (auto& inner : arr)
{
    for(auto& item : inner)
    {
        item = rand() % 100 + 1;
    }
}

Answer 2

instead of using range based for loops, you can even use functions

std::for_each(arr.begin(), arr.end(), [](array<int, 10> const& inner) {
    auto generator = []() { return rand() % 100 + 1; };
    std::generate(inner.begin(), inner.end(), generator);
}

Answer 3

#include <array>
using namespace std;

// array arr of size 5
array< array<int, 10>, 10> arr;

int main() {
  // initialize elements
  for (auto & outer_array : arr)  
  {
      for(auto & inner_array : outer_array)
      {

      }
  }
}

live: https://godbolt.org/g/6eLgBk

Answer 4

for(int i = 0; i < arr.size() ; i++)
{
   for(int j = 0; j < arr[i].size() ; j++)
   {
        arr[i][j] = rand() % 100 + 1;
   }
}