Using a pointer to an array to fill dynamic array

Question

I want to pass an array to a constructor and use its elements to fill in a dynamic array. However, I cannot understand how to go about using this array in the constructor.

I have made a function that returns a pointer to this array but I cannot use it inside the constructor for the object I am trying to create.

struct PCB
{
   private:
   int * ptr;
   public:
   PCB(int * array)
   {
      ptr=new int[3];
      for(int i=0;i<3;i++)
      {
         *(ptr+i)=*(array+i);
      }
   }
};

int * returnPtr()
{
   int blockArr[]={21,2,3};
   return blockArr;
}

int main()
{
   PCB * pcb=new PCB(returnPtr());
}

This code gives me a "segmentation fault" error using visual studio code. I simply want to be able to copy the elements of the array into the dynamic array. Where have I messed up?

The problem is that the memory of the array is freed after the execution of the function returnPtr. — Eduardo Pascual Aseff
– Eduardo Pascual Aseff, Commented Sep 15, 2019 at 4:51
Why are you using low level pointers? Why not just use std::vector and std::array? — Amadeus
– Amadeus, Commented Sep 15, 2019 at 5:03

Eduardo Pascual Aseff · Accepted Answer · 2019-09-15 04:57:46Z

1

Try this

struct PCB
{
   private:
   int * ptr;
   public:
   PCB(int * array)
   {
      ptr=new int[3];
      for(int i=0;i<3;i++)
      {
         *(ptr+i)=*(array+i);
      }
   }
};

int main()
{
   int blockArr[]={21,2,3};
   PCB * pcb=new PCB(blockArr);
}

It should fix the "segmentation fault". And remember create a destructor.

answered Sep 15, 2019 at 4:57

Eduardo Pascual Aseff

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3 Comments

jcampos12 Over a year ago

Hi thanks for the feedback. Is it possible to achieve this without getting rid of the function "returnPtr"?

Eduardo Pascual Aseff Over a year ago

well, there several approaches, one is using static int blockArr[]={21,2,3};, so the memory will remain as long as the program do

Eduardo Pascual Aseff Over a year ago

other way is declare the array in the global scope, but I don't like it that way

stylo · Accepted Answer · 2019-09-15 05:07:33Z

1

You declared blockArr as a local memory, and it will be deleted once you get out of returnPtr function. allocate byteArr as just as you allocated ptr.

int blockArr = new int[3];

edited Sep 15, 2019 at 5:07

user10957435

answered Sep 15, 2019 at 4:56

stylo

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1 Comment

Eduardo Pascual Aseff Over a year ago

blockArr was declared as local memory, no static. If were static there were no problem

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