Array initialization by constructor

Question

I have:

class first{
   private:
   int *array;

   public:
   first(int x){
     array = new int[x][10];
   }

I want to call this class by:

first class1 = new first(10);

Why it doesn't work ? How to inintialize array by size from constructor ??

In what way does it not work? Does it crash? Where? Does it not compile? What is the error you get? What happened vs. what did you expect? Details please. — i_am_jorf, Jan 06 '12 at 19:13
error: cannot convert 'int (*)[10]' to 'int*' in assignment. How to inintialize 2dimension array by size from constructor ?? I don't want to use vectors. — makeNicePlusOne, Jan 06 '12 at 20:41

score 4 · Accepted Answer · edited May 23 '17 at 10:34

4

Just this is enough:

first class1(10);

new is for when you're allocating a pointer.

first *class1 = new first(10);

Furthermore, you have an incompatibility here:

array = new int[x][10];

array is an int*, but new int[x][10] is a 2D array. I'm not sure which one you want.

For the 1D array:

int *array;
array = new int[x];

For the 2D array:

int (*array)[10];
array = new int[x][10];

That said, you might be better off using std::vector.

Side Note: Since you have memory allocation in the constructor, you should also implement a destructor, copy-constructor, and copy-assignment operator.

edited May 23 '17 at 10:34

Community

answered Jan 06 '12 at 19:13

Mysticial

1

...and a copy-assignment operator (per the [Rule of Three](http://stackoverflow.com/questions/4172722/what-is-the-rule-of-three)). But unless you particularly want to make things hard for yourself, use `std::vector`. – Mike Seymour Jan 06 '12 at 19:22
I want to initialize 2dimension array by walue from constructor. object shouldn't be an pointer. Vectors are quite another thing. How to do this ? – makeNicePlusOne Jan 06 '12 at 20:14
Answer updated. Multi-dimension arrays can get very ugly. So I suggest you use `vector > array;` unless you have a very good reason not to. – Mysticial Jan 06 '12 at 20:54

score 2 · Answer 2 · answered Jan 06 '12 at 19:22

2

You've indicate that you want a one-dimensional array (int*) but attempted to allocate a two-dimensional array (new [x][10]).

I'll assume you need one dimension.

The C++ way to do this is with vector.

#include <vector>

class first{
   private:
   std::vector<int> array;

   public:
   explicit first(int x) : array(x) {
   }
};

answered Jan 06 '12 at 19:22

Mark B

I don't need vector type. I'm interested only in array's. – makeNicePlusOne Jan 06 '12 at 20:17

2 Answers2