arrays with negative and possitive indexes, fastest access?Elements are integers

In C/C++, you can't have array indices that are negative. They are always zero-based. However, if you really need negative indices, you need have to write proxy class which translate the negative indices into zero-based indices. This, of course, leads to reduction of performance.

Just for the OP's benefit, in case it is unclear, the previous posts are the implementation details which a class might use to accomplish this. However, the interface step hasn't been mentioned, and it appears that really the question is one of getting a certain interface (since otherwise you could just transform the problem into an unsigned index in the first place). Just to fill in the details, then, you want your class to have something like

ArrayMemberType& operator[](signed index)

in order for you to use the array notation. If you put it in your header for inlining, you could conceivably have the class store whatever container is appropriate and a random-access iterator pointing at the 0 element. Then any element access is just a single addition and dereference away, just as it is for the normal array access. For a vector, with contiguous memory guarantee, the iterator is likely a bare pointer, and you should have no differences between the speed of such an implementation and a naked array.

#define LOW_BOUNDS (-100)
#define HIGH_BOUNDS (100)

/* ... */

int* array_base = (int*)malloc(sizeof(int)*(HIGH_BOUNDS - LOW_BOUNDS + 1));
int* my_int_array = array_base - LOW_BOUNDS;

/* Now you do something like:

int x = 5*my_int_array[-50];

*/

/* Cleanup: */
free(array_base);

What do you think about that? It has been written with another friend's help. The elements are integers as I want.

class A
{
private:
SomethingElse x;
int items[10]; // some kind of data
int offset=20; // (10*4)/2
public:

int& operator[](signed int i)
{
return *(items + i<<2 + offset );
}
};

int main (void)
{
A a;
int data = a[-2];
int* d_ptr = &data;
return 0;
}

KevinHall your code is exactly what I was looking for!
Thanks very much all of you.