CODEWITHSUNDEEP
c++vectorshared-ptr
Vinay Shukla
Vinay Shukla

Reputation: 1844

Segmentation fault on using shared_ptr with vectors

I am using a shared_ptr for the first time pardon me If I have made a very silly mistake and help me in overcoming this segmentation fault.

I wish to have a private vector which can be read from different classes even if the object is destroyed. Hence I read about std::shared_ptr

The code is giving a segfault in storeCounterData function

Thanks in Advance for your help !!!

main.cpp 

#include <iostream>
#include "counter.hpp"
#include "getCounter.hpp"

const int max_ports = 3;

int main()
{
  Counter *counter = new Counter(3);
  counter->age = 1;
  counter->id = 12;
  counter->pincode = 123;

  std::vector<Counter*> counterData;

  std::cout<<"inside main"<<std::endl;

  counter->storeCounterData(counter,0);
  counter->storeCounterData(counter,1);
  counter->storeCounterData(counter,2);

  std::cout<<"inside main calling getCounterData"<<std::endl;
  counter->getCounterData(counterData);

  Counter countji(3);

  countji.getCounterData(counterData);

  //getCounterData class function

   getCounter *gcount = new getCounter();

   gcount->printCounterData();

  return 0;
}

Counter.hpp 

#ifndef COUNTERHPP
#define COUNTERHPP
#include <vector>
#include <memory>

class Counter
{
private:
typedef std::shared_ptr<Counter> sharedCtr; 
std::vector<sharedCtr> vecData;
public:
Counter();
Counter(int vecSize);
int age, id, pincode;
void storeCounterData(Counter *counter,int user);
void getCounterData(std::vector<Counter*> &counter);

};

#endif

Counter.cpp 

#include "counter.hpp"
#include <iostream>
#include <vector>

Counter::Counter()
{

}

Counter::Counter(int vecSize):vecData(vecSize)
{

}

void Counter::storeCounterData(Counter *counter,int user)
{ 
  vecData[user]->age = counter->age;
  vecData[user]->id = counter->id;
  vecData[user]->pincode = counter->pincode;

  std::cout<<"vector size inside storeCounterData = "<<vecData.size()<<std::endl;
}

void Counter::getCounterData(std::vector<Counter*> &counter)
{

  std::cout<<"vector size inside getCounterData = "<<vecData.size()<<std::endl;

for (auto& c : vecData)
  {
    std::cout << c->age << std::endl;
    std::cout << c->id << std::endl;
    std::cout << c->pincode << std::endl;
  }
}

Output

Bazooka~/VECTOR$ ./a.out

inside main

Segmentation fault (core dumped)

Upvotes: 0

Views: 2332

Answers (1)

Mike van Dyke
Mike van Dyke

Reputation: 2858

In the Constructor of Counter you are creating a vector of empty shared_ptrs, i.e. there's no managed object of Counter (see (1) here).

Just change the line to:

Counter(int vecSize) : vecData(vecSize, std::make_shared<Counter>()) {}

EDIT: You are creating a vector of pointers, so I see two options here for the way you want it to work:

  1. The way you did it: Instantiate the vector with 3 shared_ptrs, but then you need to check if the pointer was already created, whenever you access the pointer.

Maybe that's the way to go. shared_ptrs are pointers aswell, you should treat them like that and always check for validity.

Counter(int vecSize) : vecData(vecSize) {} // previous constructor

void storeCounterData(Counter* counter, int user) {
  if (!vecData[user]) {
    vecData[user] = std::make_shared<Counter>();
  }
  vecData[user]->age = counter->age;
  vecData[user]->id = counter->id;
  vecData[user]->pincode = counter->pincode;

  std::cout << "vector size inside storeCounterData = " << vecData.size()
            << std::endl;
}
void getCounterData(std::vector<Counter*>& counter) {
  std::cout << "vector size inside getCounterData = " << vecData.size()
            << std::endl;

  for (auto& c : vecData) {
    if (c) {
      std::cout << c->age << std::endl;
      std::cout << c->id << std::endl;
      std::cout << c->pincode << std::endl;
    }
  }
}
  1. Use std::vector::push_back, so that you only have "valid" (you never can be sure of this) shared_ptr in the vector.

Upvotes: 2

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