I need to display an array of structures, as far as I understand, I need to use a memory shift, having a pointer to the first element of the array. When trying to fix the code, we saw the following error:

Invalid types ‘[int]’ for array subscript

my code:

#include <iostream>
#include <string.h>
using namespace std;

typedef struct Point3D{
    double x;
    double y;
    double z;
}Point3D;

Point3D createPoint3D(double xnum, double ynum, double znum){//функція створення точки
    Point3D point;
    point.x = xnum;
    point.y = ynum;
    point.z = znum;
    return point;
}

void PrintPoint(Point3D point){//використовується в інщій ф-ції, по суті внутрішня не основна функція
    cout << "(" << point.x << ","<< endl;
    cout << point.y<< ","<< endl;
    cout << point.z<< ";"<< "\n"<< endl;
    }



class Obj3D{
private:

      Point3D *array_of_points;
      int number_of_points;
public:
        void setAddPoint(Point3D point){
            *(array_of_points   sizeof(point)*number_of_points) = point;
            number_of_points  ;}

        int getNumber(){
            return number_of_points;}

        Point3D *getArray(){
        return array_of_points;}

        Obj3D(Point3D point, int number){
        number--;
        *(array_of_points   number) = point;}

        Obj3D(){
        *array_of_points = createPoint3D(0.0, 0.0, 0.0);
        number_of_points = 1;
        }

        ~Obj3D(){}
};

       void printObj(Obj3D Obj){
           for(int x = 0; x<=Obj.getNumber(); x  ){
            PrintPoint(Obj.getArray()[x]);
           }
       }


int main(int argc, char* argv[]){
    Obj3D Obj;
    Point3D point1 = createPoint3D(-0.5,-0.5,-0.5);
    Point3D point2 = createPoint3D(0.5,-0.5,-0.5);
    Point3D point3 = createPoint3D(-0.5,-0.5,0.5);
    Point3D point4 = createPoint3D(0.5,-0.5,0.5);
    Point3D point5 = createPoint3D(0.0,0.5,0.0);
    Obj.setAddPoint(point1);
    Obj.setAddPoint(point2);
    Obj.setAddPoint(point3);
    Obj.setAddPoint(point4);
    Obj.setAddPoint(point5);
    cout<<Obj.getArray();
    exit(0);
}

You can not watch the main function, it is most likely not correct, I want to deal with the functions of the output and set

CodePudding user response：

You absolutely don't need to memory shift

*(array_of_points   sizeof(point)*number_of_points) = point;

C is not that complicated, just

array_of_points[number_of_points] = point;

Because the compiler knows the type involved, Point3D, it's quite capable of working out the memory shift by itself. Also by the rules of C *(p n) is exactly equivalent to p[n] but generally prefer the latter because it is easier to read.

Other errors (which you'll find out when you run the code). Class Obj3D has an uninitialised pointer array_of_points. You use the pointer, e.g. here

Obj3D(){
    *array_of_points = createPoint3D(0.0, 0.0, 0.0);
    number_of_points = 1;
}

but you never give the pointer a value. So that is going to crash your program.

You need to allocate memory using new for your pointer to point at. That doesn't happen automatically. E,g,

Obj3D() {
    array_of_points = new Point3D[100]; // allocate 100 points
    array_of_points[0] = createPoint3D(0.0, 0.0, 0.0);
    number_of_points = 1;
}

CodePudding user response：

The problem(besides the typo of missing )) is that you're not calling method getArray and instead using operator[].

To solve this call the method getArray by replacing Obj.getArray[x] with Obj.getArray()[x] as shown below:

//---------------------vv---v---->parenthesis added for calling and also for closing
PrintPoint(Obj.getArray()[x]);

Working demo