Initialize public attributes with argument from class constructor in c++

Question

I have a class implemented in a .cpp file as follow :

#include <ctime>
#include <iostream>

// les 3 lib boost/random nécessaire a généré les radiuses
#include "boost/random/mersenne_twister.hpp"
#include "boost/random/normal_distribution.hpp"
#include "boost/random/variate_generator.hpp"
// la lib boost fournissant des arrays multidimensionnels
#include "boost/multi_array.hpp"

#include "porenetwork.h"

using namespace std;

typedef boost::random::mt19937 ENG;
typedef boost::normal_distribution<double> DIST;   // Normal Distribution
typedef boost::variate_generator<ENG,DIST> GEN;    // Variate generator

typedef boost::multi_array<bool, 3> StateNetworkType;
typedef boost::multi_array<double, 3> RadiusNetworkType;
typedef StateNetworkType::index index;
typedef boost::multi_array_types::index_range range;



PoreNetwork::PoreNetwork(int esize)
{
cout << "esize = " << esize << endl;
Size = esize;
StateNetworkType States(boost::extents[Size][Size][Size]);
RadiusNetworkType Radiuses(boost::extents[Size][Size][Size]);

// initialise the Radiuses
ENG eng;
eng.seed(static_cast<unsigned int>(std::time(0)));
DIST dist(0,1);
GEN gen(eng, dist);

for(index i = 0; i != Size; ++i) 
    for(index j = 0; j != Size; ++j)
        for(index k = 0; k != Size; ++k)
            Radiuses[i][j][k] = gen();

}

int PoreNetwork::getSize() {return Size;}

And defined in a header .h file as follow :

#ifndef PORENETWORK_H
#define PORENETWORK_H

#include "boost/multi_array.hpp"

typedef boost::multi_array<bool, 3> StateNetworkType;
typedef boost::multi_array<double, 3> RadiusNetworkType;

class PoreNetwork
{
public:
    PoreNetwork(int esize);
    int getSize();
    StateNetworkType States;
    RadiusNetworkType Radiuses;

private:
    int Size;
    /* add your private declarations */
};

#endif /* PORENETWORK_H */

My problem is that the Attributes PoreNetwork::Radiuses and PoreNetwork::States do not seem to get initialized when I call this from my main.cpp.

As I understand it, the Radiuses and States in my .cpp are not the ones defined in my headers file because I re-define them.

My problem is : how do I define and initialize these 2 attributes in my class, knowing that they are Boost::multi_array and that their constructor takes as input a parameters that my class constructor takes also.

i.e : my PoreNetwork class' constructor takes 1 argument esize that is an int, that is also the argument of the constructor for its attributes Radiuses and States.

What you do in your constructor is declaring local variables and initializing them. — Some programmer dude, Nov 09 '12 at 08:02

billz · Accepted Answer · 2012-11-09T08:06:50.770

The best way to initialise members is to use initialise list. But you still need to pay attention to the member declaration order and initialise orders.

class PoreNetwork
{
private: 
    int Size;  // note, put Size in front of States/Radiuses members
public:
    PoreNetwork(int esize);
    int getSize();
    StateNetworkType States;
    RadiusNetworkType Radiuses;
};

PoreNetwork::PoreNetwork(int esize)
: Size(esize),        // important to initialise Size first
  States(boost::extents[Size][Size][Size]),
  Radiuses(boost::extents[Size][Size][Size]) 
{
  cout << "esize = " << esize << endl;
}

If your do not initialise Size first, it's undefined behavior to initialise States and Radiuses and Size has not initialised with yet.

 PoreNetwork::PoreNetwork(int esize)
    : States(boost::extents[Size][Size][Size]),      // Undefined behavior as Size is not initialised yet
      Radiuses(boost::extents[Size][Size][Size]),
      Size(esize)

If yo don't put Size in in front of States/Radiuses in the member list, you get compiler warning.

score 0 · Answer 2 · answered Nov 09 '12 at 07:51

0

use the initializer list:

PoreNetwork::PoreNetwork(int esize) :
  States(boost::extents[esize][esize][esize]),
  Radiuses(boost::extents[esize][esize][esize]),
  Size(esize) 
{
...
}

answered Nov 09 '12 at 07:51

stijn

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hmm, a problem, you should put Size(esize) on the top of initialise list, otherwise it's undefined behavior to initialise States and Radiuses – billz Nov 09 '12 at 07:55
ah good point, I meant to replace Size with esize there but forgot.. fixed; Size(esize) cannot be put on top because members should be initialized in the order declared, and in the class definition Size comes last – stijn Nov 09 '12 at 07:55

score 0 · Answer 3 · answered Nov 09 '12 at 07:51

Member variables constructors are called like this:

PoreNetwork::PoreNetwork(int esize) :
  States(boost::extents[esize][esize][esize]),
  Radiuses(boost::extents[esize][esize][esize])
{
  ...
}

This means that it's hard to work with the constructor arguments inside the body before you apply them to your member variables. Using a function like boost::extents if often the only option if you can't call resize() (or something similar).

Initialize public attributes with argument from class constructor in c++

3 Answers3