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POC++ populating vectors inside class constructors
 

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  1. POC++ populating vectors inside class constructors
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    <p>I have troubling addressing elements inside objects of Class3, please look at this simplified classes:</p> <pre><code>class Class1 { public: std::vector&lt;Class2&gt; c2v; Class1(); }; class Class2 { Class1 *instance; int id; public: std::vector&lt;Class3&gt; c3v; Class2 ( Class1 *instance, int id ); }; class Class3 { Class1 *instance; int id; public: Class3 ( Class1 *instance, int id ); }; </code></pre> <p>And their constructors:</p> <pre><code>Class1::Class1() { for ( int i = 0; i &lt; noi; ++i ) { c2v.push_back ( Class2 ( this, i ) ); } } Class2::Class2 ( Class1 *instance, int id ) { this-&gt;instance = instance; this-&gt;id = id; for ( int k = 0; k &lt; nok; ++k ) { c3v.push_back ( Class3 ( this-&gt;instance, k ) ); } } </code></pre> <p>In main() an object of Class1 is instantiated with its default constructor. Therefore it creates a vector c2v and fills it with 'noi' objects of Class2.</p> <p>At the same time, when the objects of Class2 are being put into c2v vector, they're instantiated and each one creates a vector c3v and fills it with 'non' objects of Class3.</p> <p>The code compiles fine but at runtime when accessing public attributes of Class2 from Class3 objects (via <code>this-&gt;instance-&gt;c2v[0].getSomeAttribute()</code>) the program stops with a EXC_BAD_ACCESS.</p> <p>Inspecting with a debugger shows that the pointer to <code>c2v[0]</code> gets corrupted (its value becomes 0x0).</p> <p>I'm a newbie of C++ I was wondering what is the error when trying to instantiate vectors this way. Should I only declare the vectors and populate them in a separate function called after the creation of all instances of Class2 and Class3 is finished?</p> <p>I'm adding some actual code, hope it won't be too long to read (please understand I've omitted some forward declarations and preprocessor directives):</p> <pre><code>// global variables extern char *filename; //not used extern int nodes; extern int numProdotti; extern int classe; //not used extern int maxNumRange; //not used extern int *numRanges; extern int *list ; extern int *typeProdMarket; extern int totalQtyDemand; //not used extern int totNumRanges; //not used extern struct product { int qty; int cost; } **prodMarket; extern struct range { int discount; int startOfRange; } **rangeMarket; //not used int main ( int argc, char *argv[] ) { Ctqd instance; instance.runOpt(); } class Ctqd { void greedySimple(); void greedySimpleReverse(); void greedyFromY(); void greedyByNiceness1(); void greedyByNiceness2(); void greedyByStepTier1(); void greedyByStepTier2(); void randomLocalSearch1(); void LocalSearch2opt(); public: std::vector&lt;Item&gt; items; std::vector&lt;Supplier&gt; suppliers; Solution *solution; Ctqd(); ~Ctqd(); void runOpt(); }; class Supplier { Ctqd *instance; int id; int refTotQty; int refDiscount; int refDiscountTier; double refTotPrice; double refUnitPrice; double niceness; int purTotQty; int purDiscount; int purDiscountTier; public: std::vector&lt;Offer&gt; offers; Supplier ( Ctqd *instance, int id ); int getId(); int getRefTotQty(); int getRefDiscount(); int getRefDiscountTier(); double getRefTotPrice(); double getRefUnitPrice(); double getNiceness(); int getPurTotQty(); int getPurDiscount(); int getPurDiscountTier(); void updateStats(); }; class Offer { Supplier *supplier; int id; int refQty; double refPrice; double niceness; int purQty; public: Offer ( Supplier *supplier, int id ); int getId(); int getRefQty(); double getRefPrice(); double getNiceness(); int getPurQty(); void setPurQty ( int qty ); int remainingQty(); }; Ctqd::Ctqd() { // constructing items vector for ( int k = 0; k &lt; numProdotti; ++k ) { items.push_back ( Item ( this, k ) ); } // constructing suppliers vector for ( int i = 0; i &lt; nodes; ++i ) { suppliers.push_back ( Supplier ( this, i ) ); } // building solution solution = new Solution ( this ); } Supplier::Supplier ( Ctqd *instance, int id ) { this-&gt;instance = instance; this-&gt;id = id; // computing total reference quantity refTotQty = 0; for ( int k = 0; k &lt; numProdotti ; ++k ) { refTotQty += std::min ( list[ k ] , prodMarket[ this-&gt;id ][ k ].qty ); } // computing reference discount coefficients refDiscount = 0; refDiscountTier = 0; for ( int r = 0; r &lt; numRanges[ this-&gt;id ]; ++r ) { if ( refTotQty &lt; rangeMarket[ this-&gt;id ][ r ].startOfRange ) { break; } else { refDiscount = rangeMarket[ this-&gt;id ][ r ].discount; refDiscountTier = r; } } //computing total reference price refTotPrice = 0; for ( int k = 0; k &lt; numProdotti ; ++k ) { refTotPrice += prodMarket[ this-&gt;id ][ k ].cost * std::min ( list[ k ] , prodMarket[ this-&gt;id ][ k ].qty ); } refTotPrice = refTotPrice * ( 1.000 - refDiscount / 100.000 ); //computing reference unit price refUnitPrice = refTotPrice / refTotQty; //computing supplier niceness niceness = refTotQty / refUnitPrice; purTotQty = 0; purDiscount = 0; purDiscountTier = 0; // building offers vector for ( int k = 0; k &lt; numProdotti; ++k ) { offers.push_back ( Offer ( this, k ) ); } } Offer::Offer ( Supplier *supplier, int id ) { this-&gt;supplier = supplier; this-&gt;id = id; // computing reference quantity refQty = std::min ( list[ this-&gt;id ] , prodMarket[ this-&gt;supplier-&gt;getId() ][ this-&gt;id ].qty ); // computing reference price refPrice = prodMarket[ this-&gt;supplier-&gt;getId() ][ this-&gt;id ].cost * ( 1.000 - this-&gt;supplier-&gt;getRefDiscount() / 100.000 ); // computing niceness of the offer niceness = refQty / ( ( prodMarket[ this-&gt;supplier-&gt;getId() ][ this-&gt;id ].cost + refPrice ) / 2 ); // init purQty to 0 purQty = 0; } </code></pre> <p>This is where I get the EXC_BAD_ACCESS:</p> <pre><code>int Offer::remainingQty() { return prodMarket[ supplier-&gt;getId() ][ id ].qty - purQty; } </code></pre> <p>I've done some experiments: Changed the vectors in the Ctqd class and in the Supplier class to vectors of pointer to objects. Problem was solved only partially. Still had a EXC_BAD_ACCESS when constructing the offers objects.</p> <p>The constructor for Offer class needs data from the Supplier object that created it. I thought that accessing that data while the suppliers vector was still being populated could lead to problems, so I created a little initialize() function in the supplier:</p> <pre><code>void Supplier::initialize() { // constructing offers vector for ( int k = 0; k &lt; numProdotti; ++k ) { offers.push_back ( new Offer ( this-&gt;instance, id, k ) ); } } </code></pre> <p>And added this at the end of the Ctqd class constructor:</p> <pre><code>// init newly built objects for ( int i = 0; i &lt; nodes; ++i ) { suppliers[i]-&gt;initialize(); } </code></pre> <p>Now things seem to be working fine. But i still didn't figure out what the problem exactly was.</p>
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    1. USMarco Romano
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    1. COWhat are you **really** trying to do? what is the policy for pointer ownership?
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      1. USKarl Knechtel
    2. COClass1 is just a container for the problem instance. Class2 represents suppliers from which I can buy goods. Class3 represent the offers for goods the suppliers make. Therefore I put all the suppliers in array c2v and each supplier creates its own c3v array and fill it with its offers. Pointer ownerships are all public.
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      1. POC++ populating vectors inside class constructors
      1. USMarco Romano
    3. COThis example works for me. You should post a complete compilable example that gives the error.
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      1. UShansmaad
 

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