a nicer way to create structs in a loop

Question

Hi guys, I haven't coded in C++ in ages. And recently, I'm trying to work on something involving structs. Like this

typedef struct{
    int x;
    int y;
} Point;

Then in a loop, I'm trying to create new structs and put pointers to them them in a list.

Point* p;
int i, j;
while (condition){
    // compute values for i and j with some function...
    p = new Point;
    p* = {i, j}; //initialize my struct.
    list.append(p); //append this pointer to my list. 
} 

Now, my question is it possible to simplify this? I mean, the pointer variable *p outside of the loop and calling p = new Point inside the loop. Isn't there a better/nicer syntax for this?

Answer 1

Sure:

Point * p  = new Point;

You should probably also give your Point class a constructor:

struct Point {      // note no need for typedef
    int x;
    int y;
    Point( int ax, int ay ) : x( ax ), y( ay ) {}
};

so that you can say:

Point * p  = new Point( i, j );

You may also want to make your list a list of Point values, rather than pointers, in which case you can avoid using dynamic allocation with new - always something to be avoided wherever possible in C++.

Answer 2

As structs are classes with public members by default, you could even create a constructor within the struct and initialize your point object within the loop like this:

Point* p = new Point(i,j);

Answer 3

The struct can have a constructor like:

struct Point{
    Point(int ax, int ay):x(ax), y(ay){}
    int x;
    int y;
};

and then the function can look like:

int i, j;
while (condition)
{
    list.append(new Point(i,j));
} 

Answer 4

I would venture a guess that it is extremely unlikely you really need to allocate something like a Point dynamically.

Most likely you want to add a constructor and store them by value:

list<Point> list;
list.append(Point(x, y));

Answer 5

I recommend the Factory approach. Assuming that "Point" will be the base class of many objects, you can have a "Factory" that would return pointers.

Ex:

struct Point
{
        Point(int mx, int my):x(mx),y(my) {}
        int x;
        int y;
};

// Circle, Polygon, etc.

class Factory
{
public:
        static Point *getPoint(int mx, int my) { return new Point(mx, my); }
// Circle, Polygon, etc
};

Then in code someplace:

while(cond)
{
 list.append(Factory::getPoint(i, j));
}