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 ??

• i_am_jorf: 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.
• makeNicePlusOne: 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.

Answer 1

Just this is enough:

first class1(10);

new is for when you're allocating a pointer.

first *class1 = new first(10);

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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.

• Mike Seymour: ...and a copy-assignment operator (per the Rule of Three). But unless you particularly want to make things hard for yourself, use std::vector.
• makeNicePlusOne: 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 ?
• Mysticial: Answer updated. Multi-dimension arrays can get very ugly. So I suggest you use vector<vector<int> > array; unless you have a very good reason not to.

Answer 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) {
 }
};

• makeNicePlusOne: I don't need vector type. I'm interested only in array's.