2

How can I store million objects into array without error? I'm playing with a 3dEngine in C++ , all works nice and fast but i can't add more than 50K Objects . Object contains 3 vector and colors and some useful method . Some Help ?

enter image description here

#include <iostream>

using namespace std;

class Myc{
    public:
    double x,y,z;
    Myc(double _x=0 ,double _y=0,double _z=0){
        x=_x;y=_y;z=_z;
    }
};

int main(){
    int i; 
    int N=151000;
    Myc pts[N];
    for (i=0;i<N;i++){
        pts[i] = Myc(1,1,1);
    }
    
    cout << pts[999].x <<endl;
    return 0;
}

output:

1                                                                                                                                                                                                                                                                                                                                                                              
...Program finished with exit code 0

But using int N=1151000;

the output is :

Segmentation fault (core dumped)

How can I store million objects into array without error? Thanks .

Mario Abbruscato
  • 819
  • 1
  • 7
  • 9
  • 2
    Classic example of stack overflow. Default stack size is limited (for example 1 MB on windows). Use `Myc * pts = new Myc[N];` or `std::vector pts; pts.resize(N);` – rafix07 Feb 11 '21 at 06:21
  • 2
    Array data is stored on the stack, which does not have enough space for a million elements. You could use `std::vector` or perhaps even a dynamic array. – mediocrevegetable1 Feb 11 '21 at 06:22

3 Answers3

3

You can allocate the memory on the heap (dynamically allocate it). Currently you are getting stack overflow.

Another way is to do: ulimit -s unlimited on any Linux system to increase the stack size but I advise you to go with the first option.

Silidrone
  • 1,471
  • 4
  • 20
  • 35
2

You can use a std::vector like this:

#include <vector>

class Myc{
    public:
    double x,y,z;
    Myc(double _x=0 ,double _y=0,double _z=0){
        x=_x;y=_y;z=_z;
    }
};

int main(){
    int i; 
    int N=151000;

    std::vector<Myc> pts(N); // stores its data in the free store (heap)

    for (i=0;i<N;i++){
        pts[i] = Myc(1,1,1);
    }
    
    cout << pts[999].x <<endl;
    return 0;
}

A std::vector stored its internal array on the free store (heap) which has a lot more memory that the function stack, which is where local variables like your array are kept.

Galik
  • 47,303
  • 4
  • 80
  • 117
0

use a std::vector and insert calling the pts.emplace_back method

int main(){
    int i; 
    int N = 9999999;
    std::vector<Myc> pts;
    for (i = 0; i < N; i++)
    {
        pts.emplace_back(Myc(1, 1, 1));
    }
    
    cout << pts[999].x <<endl;
    return 0;
}
ΦXocę 웃 Пepeúpa ツ
  • 47,427
  • 17
  • 69
  • 97
  • 1
    When there are `9999999` objects it's going to be signifcantly better to reserve the space needed, `pts.reserve(N);`. – john Feb 11 '21 at 07:16