CODEWITHSUNDEEP
c++pointersvector
Dmitry Kazakov
Dmitry Kazakov

Reputation: 165

Vector fails to get initialized

I am trying do initialize a vector of self-defined type dataCard:

vector<dataCard> dataSet;
dataSet.reserve(200);

However the compiler doesn't allow me to do that indicating an error at the second line (where I try to reserve space for the container):

required from here

However when I change the declaration to the following

vector<dataCard*> dataSet;

it starts working.

What could be the reason for the compiler not allowing me to use my type as it is, but letting me to use a pointer to the type? I actually need a vector of objects, not pointers to them.

EDIT

Header file of dataCard

#include <card.h>


class dataCard {
    char* name; // name according to the filename
    char Class; // Classes: 2, 3, 4, 5, 6, 7, 8, 9, T, J, Q, K, A
    double distanceToQuery;
public:
    void resetDistance();
    int numBlackTotal (bitmap* bmp);
    bitmap image;
    int numOfBlackPixels;
    char* getName();
    void setName(char* n);
    void setClass (char* c);
    char* getClass();
    void setDistance(double distance);
    double getDistance ();
    dataCard(const char* fname);
    dataCard();
    virtual ~dataCard();
};

Here's an error message from compiler

/usr/include/c++/4.7/bits/stl_uninitialized.h:77:3:   required from ‘static _ForwardIterator std::__uninitialized_copy<_TrivialValueTypes>::__uninit_copy(_InputIterator, _InputIterator, _ForwardIterator) [with _InputIterator = dataCard*; _ForwardIterator = dataCard*; bool _TrivialValueTypes = false]’
/usr/include/c++/4.7/bits/stl_uninitialized.h:119:41:   required from ‘_ForwardIterator std::uninitialized_copy(_InputIterator, _InputIterator, _ForwardIterator) [with _InputIterator = dataCard*; _ForwardIterator = dataCard*]’
/usr/include/c++/4.7/bits/stl_uninitialized.h:260:63:   required from ‘_ForwardIterator std::__uninitialized_copy_a(_InputIterator, _InputIterator, _ForwardIterator, std::allocator<_Tp>&) [with _InputIterator = dataCard*; _ForwardIterator = dataCard*; _Tp = dataCard]’
/usr/include/c++/4.7/bits/stl_vector.h:1112:8:   required from ‘std::vector<_Tp, _Alloc>::pointer std::vector<_Tp, _Alloc>::_M_allocate_and_copy(std::vector<_Tp, _Alloc>::size_type, _ForwardIterator, _ForwardIterator) [with _ForwardIterator = dataCard*; _Tp = dataCard; _Alloc = std::allocator<dataCard>; std::vector<_Tp, _Alloc>::pointer = dataCard*; std::vector<_Tp, _Alloc>::size_type = long unsigned int]’
/usr/include/c++/4.7/bits/vector.tcc:76:70:   required from ‘void std::vector<_Tp, _Alloc>::reserve(std::vector<_Tp, _Alloc>::size_type) [with _Tp = dataCard; _Alloc = std::allocator<dataCard>; std::vector<_Tp, _Alloc>::size_type = long unsigned int]’
/home/ppsadm01/Documents/vgv/src/main.cc:145:22:   required from here
/usr/include/c++/4.7/bits/stl_construct.h:85:7: error: no matching function for call to ‘dataCard::dataCard(const dataCard&)’

Upvotes: 2

Views: 97

Answers (2)

TobiMcNamobi
TobiMcNamobi

Reputation: 4813

As the error message suggests you need to implement the copy constructor dataCard::dataCard(const dataCard&). You need that because for example vector<dataCard>::push_back() will copy dataCard instances.

When you write the copy constructor, be careful that all member variables get copied - in the right way. So an example implementation could be

dataCard::dataCard(const dataCard &rhs)
{
    strcpy(name, rhs.name);
    Class = rhs.Class;
    distanceToQuery = rhs.distanceToQuery;
    image = rhs.image; // make sure that this is OK!
}

Upvotes: 2

Erika
Erika

Reputation: 416

If the compiler does not know the size of a dataCard object, it cannot reserve space for it. A pointer however is always a known size so it can reserve space for that.

My guess is that the compiler does not know the exact size of a dataCard object. If for example the bitmap type object is of variable size, then the compiler would not know what size dataCard would be.

Upvotes: 2

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