Vector push_back of one object results in a vector of enormous size

Question

i'm working on a project in c++, and I have a vector of objects, where I want to push_back an object on the existing vector. However, when checking the size before and after the object is added, the size goes from 0 to 12297829382473034412 which puzzles me greatly. The code in question is the addCommodity function below. (I have created a smaller example of the same problem further down, so skip to " SMALL PROBLEM ")

void Instance::addCommodity(std::vector<std::string> & tokens) {
  /*if(tokens.size()!=5){
    std::cerr << "Error in commodity data format"<< std::endl;
    exit(-1);
  }*/
  // size_t so = std::atoi(tokens[1].c_str());
  // size_t si = std::atoi(tokens[2].c_str());
  // size_t demand = std::atoi(tokens[3].c_str());
  // size_t ti = std::atoi(tokens[4].c_str());
  std::cout << "size: " << this->_commodities->size() << "\n"; 

  this->_commodities->push_back(Commodity(1,2,3,4));  // ???

  std::cout << "size: " << this->_commodities->size() << "\n";
}

Here I have commented out the parts of the code which are used to read data from a string which was loaded from a file. Commodity is defined as follows:

#include "commodity.h"

Commodity::Commodity(size_t so, size_t si, size_t d, size_t ti):
  _source(so),
  _sink(si),
  _demand(d),
  _maxTime(ti)
{}

Commodity::~Commodity(){}

size_t Commodity::getSource() const{
  return _source;
}

size_t Commodity::getSink() const {
  return _sink;
}

size_t Commodity::getDemand() const {
  return _demand;
}

size_t Commodity::getTime() const {
  return _maxTime;
}

Where Instance is initialised as:

Instance::Instance(std::shared_ptr<Param> p, size_t n):
  _params(p),
  _nNodes(n)
{
  this->_commodities.reset(new std::vector<Commodity>());
  this->_arcs.reset(new std::vector<Arc>());
  }

As mentioned before my issue lies in the addCommodity code, when trying to push_back a Commodity. Hopefully this is enough code to identify any stupid mistakes that I have made. I left out most of the other code for this project as it doesn't seem to have an impact on the addCommodity function.

The output received when calling the function is:

size: 0
size: 12297829382473034412

SMALL PROBLEM

Instead of showing all the code, I have run the push_back on the vector in main:

#include <iostream>
#include <memory>
#include <sys/time.h>
#include <vector>


#include "commodity.h"

int main(int argc, char* argv[]){


 std::shared_ptr< std::vector<Commodity>> commodities;

  commodities.reset(new std::vector<Commodity>());

  std::cout << "size: " << commodities->size() << "\n";

  size_t a = 1;
  size_t b = 2;
  size_t c = 3;
  size_t d = 4;

  commodities->emplace_back(Commodity(a,b,c,d));

  std::cout << "size: " << commodities->size() << std::endl;

  return 0;

}

This is basically a smaller instance of the same code. The commodity cpp and h files are as follows:

#include "commodity.h"

Commodity::Commodity(size_t so, size_t si, size_t d, size_t ti):
  _source(so),
  _sink(si),
  _demand(d),
  _maxTime(ti)
{}

Commodity::~Commodity(){}

size_t Commodity::getSource() const{
  return _source;
}

size_t Commodity::getSink() const {
  return _sink;
}

size_t Commodity::getDemand() const {
  return _demand;
}

size_t Commodity::getTime() const {
  return _maxTime;
}

The header file:

#ifndef CG_MCF_COMMODITY_H
#define CG_MCF_COMMODITY_H

#include <stdlib.h>

class Commodity {

 public:

  Commodity(size_t so, size_t si, size_t d, size_t t);

  ~Commodity();

  size_t getSource() const;

  size_t getSink() const;

  size_t getDemand() const;

  size_t getTime() const;

 private:

  size_t _source;

  size_t _sink;

  size_t _demand;

  size_t _maxTime;

};

#endif /*CG_MCF_COMMODITY_H*/

The output received when calling the function is:

size: 0
size: 12297829382473034412

Answer 1

Your Commodity class violates the rule of 0/3/5 .

Your code (inexplicably) does this:

commodities->emplace_back(Commodity(a,b,c,d));

This is really strange. Presumably, you're calling emplace_back to avoid having to construct a separate Commodity from the one in the vector. But you force that to happen by explicitly constructing a separate Commodity as the parameter to emplace_back .

That invokes Commodity 's copy constructor to construct the Commodity in the vector as a copy of the one you explicitly created. Except Commodity doesn't have one. Most likely, the real Commmodity class needs one, since it has a destructor.