Initializing an array inside a structure from another array in C++ [closed]

Question

struct sample {
    int x;
    int y;
    int arr[10];
};

int arr2[10] = {0, 1, 2, 4, 3, 2, 2, 1, 5, 5};

int a = 19; 
int b = 22;
struct sample* samp = new sample;
samp->x = a;
samp->y = b;
samp->arr = ??

In the above example, I need to initialize array inside the structure arr[10] with the elements of arr2[10].

How to do it in C++??

Answer 1

How to do it in C++??

The simplest solution is to use std::copy as was said by others. Do not use memcpy in C++, as std::copy does the same for PODs but also is applicable for non-PODs and just Does The Right Thing. If the type in your array changes one day, you would have to revisit all places where you do such a copy and replace the memcpy. (And you will miss one of the places and have a hard time to find the bug). Using memcpy in C++ has no benefits, so use std::copy from the start.

The better solution would be to use C++ data structures, in this case, use std::array

#include <array>
struct sample {
      int x;
      int y;
      std::array<int, 10> arr; //C++ array instead of plain C array
    };

int main()
{
    std::array<int, 10> arr2 = {0, 1, 2, 4, 3, 2, 2, 1, 5, 5};

    int a = 19; 
    int b = 22;

    // 1: no need to say "struct sample*" since C++98
    // 2: prefer to use smart pointers..
    //sample* samp = new sample; 
    std::unique_ptr<sample> samp(new sample());
    samp->x = a;
    samp->y = b;
    samp->arr = arr2; //it's as easy as it should be!

    // 3: ... so ypu can't forget to delete!
    //delete samp;
}

Edit: I used unique_ptr here, although in this little example you don't need to use heap allocation at all. To bring in Grijesh's initialization in as well:

int main()
{
    std::array<int, 10> arr2 = {0, 1, 2, 4, 3, 2, 2, 1, 5, 5};

    int a = 19; 
    int b = 22;

    sample samp = {a, b, arr2}; //done!
}

no allocation, no cleanup, no element-wise assignment needed.

Answer 2

you can use memcpy:

memcpy(sample->arr,arr2,sizeof(int) * 10)

But I would suggest using std::vector for both.

Answer 3

Copy array using for loop,

for(int i=0; i<10; i++) {
    samp->arr[i]=arr2[i];
}