CODEWITHSUNDEEP
c++pointersstruct
Kelly Flet
Kelly Flet

Reputation: 564

Accessing members of struct from queue of pointers

I am having an issue trying to assign a value to a member variable of my struct, PCB. I am using a queue of pointers to my struct. So I first dereference the pointer passed to the inititiate_process function, and next try to deference the pointer from the ready_queue to access the member variable. How do I access this member variable? I am getting an 'invalid type conversion' on this line of code (static_cast<PCB*>(ready_queue->front()))->next_pcb_ptr = &pcb;.

Here is my struct in a header file

#ifndef PCB_H
#define PCB_H

struct PCB {
    int p_id;
    int *page_table_ptr;
    int page_table_size;
    int *next_pcb_ptr;
};
#endif // !PCB_H

Here is my source cpp file

#include <iostream>
#include <queue>
#include "PCB.h"

using namespace std;

void initiate_process(queue<int*>* ready_queue) {
    // allocate dynamic memory for the PCB
    PCB* pcb = new PCB;

    // assign pcb next
        if(!(ready_queue->empty())){
            // get prior pcb and set its next pointer to current
            (static_cast<PCB*>(ready_queue->front()))->next_pcb_ptr = &pcb;
        }
}

void main(){
    queue<int *> ready_queue;
    initiate_process(&ready_queue);
}

Upvotes: 1

Views: 1070

Answers (1)

Snohdo
Snohdo

Reputation: 156

Are you sure you need the static_cast? I suggest in your PCB.h you should instead use

struct PCB *next_pcb_ptr;

and then in the main part of the program and initiate_process, use struct PCB * instead of int *

void initiate_process(queue<struct PCB *> *ready_queue) {

  // allocate dynamic memory for the PCB
  struct PCB *pcb = new struct PCB;

  // assign pcb next
  if(!(ready_queue->empty())){

    (ready_queue->front())->next_pcb_ptr = pcb;

  }

}

Upvotes: 1

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