Assign array to array

Question

So I am playing around with some arrays, and I cannot figure out why this won't work.

int numbers[5] = {1, 2, 3};
int values[5] = {0, 0, 0, 0, 0};
values = numbers; 

The following error appear:

Error   1   error C2106: '=' : left operand must be l-value c:\users\abc\documents\visual studio 2012\projects\consoleapplication7\consoleapplication7\main.cpp 9   1   ConsoleApplication7

Why can't I do like that? What does the error mean?

Answer 1

Arrays have a variety of ugly behavior owing to C++'s backward compatibility with C. One of those behaviors is that arrays are not assignable. Use std::array or std::vector instead.

#include <array>
...
std::array<int,5> numbers = {1,2,3};
std::array<int,5> values = {};
values = numbers;

If, for some reason, you must use arrays, then you will have to copy the elements via a loop, or a function which uses a loop, such as std::copy

#include <algorithm>
...
int numbers[5] = {1, 2, 3};
int values[5] = {};
std::copy(numbers, numbers + 5, values);

As a side note, you may have noticed a difference in the way I initialized the values array, simply providing an empty initializer list. I am relying on a rule from the standard that says that if you provide an initializer list for an aggregate, no matter how partial, all unspecified elements are value initialized. For integer types, value initialization means initialization to zero. So these two are exactly equivalent:

int values[5] = {0, 0, 0, 0, 0};
int values[5] = {};

Answer 2

You can't assign arrays in C++, it's stupid but it's true. You have to copy the array elements one by one. Or you could use a built in function like memcpy or std::copy.

Or you could give up on arrays, and use std::vector instead. They can be assigned.