How can I copy a part of an array to another array in C++?

Question

This is the same question asked in C# but i need for C++

How can I copy a part of an array to another array?

Consider I\'m having

    int[] a = {         


        

Answer 1

Yes, using st standard library algorithm copy:

#include <algorithm>

int main()
{
  int array[5] = { 1,2,3,4,5 }; // note: no int[] array
  int *b = new int[3];
  std::copy(array+1, array+4, b); 
  // copies elements 1 (inclusive) to 4 (exclusive), ie. values 2,3,4
}

Answer 2

Assuming you want a dynamically-allocated array as in the C# example, the simplest way is:

std::vector<int> b(a.begin() + 1, a.begin() + 4);

This also has the advantage that it will automatically release the allocated memory when it's destroyed; if you use new yourself, then you'll also need to use delete to avoid memory leaks.

Answer 3

Yes, use std::copy:

std::copy(a + src_begin_index,
          a + src_begin_index + elements_to_copy,
          b + dest_begin_index);

The equivalent of your C# example would be:

std::copy(a + 1, a + 4, b);

Answer 4

For simple C-style arrays you can use memcpy:

memcpy(b, &a[1], sizeof(int) * 3);

This line copies sizeof(int) * 3 bytes (i.e. 12 bytes) from index 1 of a, with b as a destination.

Answer 5

There is the C memcpy command, which you can use like this:

memcpy(destinationArray, sourceArray, sizeof(*destinationArray) * elementsToCopy);

There is also std::copy, which is a more C++ way of doing it:

std::copy(source, source + elementsInSource, destination);

Note that neither of these functions check to make sure that enough memory has been allocated, so use at your own risk!