CODEWITHSUNDEEP
c++classconstructorderived-class
Elliot Hatch
Elliot Hatch

Reputation: 1110

Derived Class not Calling Entire Base Constructor

I'm sure this is just some stupid syntax error I'm making, but when my class CNeck derived from CLimb calls its default constructor, CNeck() everything works as expected. When it calls a different constructor CNeck(*parent) it seems to call about half of the specified base constructor, then gives uses the compiler default constructor or something weird.

main.cpp

int _tmain(int argc, _TCHAR* argv[])
{
    CNeck neck01;
    CLimb *ptr;
    ptr = &neck01;
    CNeck neck02(ptr);
    return 0;
}

limb.h (parent class)

class CLimb
{
public:
    CLimb(void);
    CLimb(CLimb *_parent);
    ~CLimb(void);

    float cut;
    float bone;
    float resistance;
    //attributes
    bool isBurned;
    bool isBleeding;
    bool isOnFire;
    bool isNeedFirstaid;

    CLimb *parent;
};

limb.cpp (parent class)

#include "limb.h"

CLimb::CLimb(void) :
    cut(10),
    bone(10),
    resistance(10),
    //attributes
    isBurned(0),
    isBleeding(0),
    isOnFire(0),
    isNeedFirstaid(0)
{
    parent = NULL;
}

CLimb::CLimb(CLimb *_parent) :
    cut(10),
    bone(10),
    resistance(10),
    //attributes
    isBurned(0),
    isBleeding(0),
    isOnFire(0),
    isNeedFirstaid(0)

{
    parent = _parent;
}

CLimb::~CLimb(void)
{
}

neck.h (child class)

#include "limb.h"
class CNeck :
    public CLimb
{
public:
    CNeck(void);
    CNeck(CLimb *_parent);
    ~CNeck(void);
};

neck.cpp (child class)

#include "Neck.h"


CNeck::CNeck(void)
{
}

CNeck::CNeck(CLimb *_parent) : CLimb(*_parent)
{
}

CNeck::~CNeck(void)
{
}

As you can see, the child class doesn't do anything other than call the parent's constructor, yet when I step through the program I get the following results:
CNeck neck01;: normal
CNeck neck02(ptr);: values cut, bone, resistance, and isBurned all have proper values, but isBleeding, isOnFire, and isNeedFirstaid all equal 1 instead of zero. The body of CNeck::CNeck(*parent) is still executed.
When I was testing and called CLimb limb(ptr); instead of CNeck neck02(ptr); all the values were assigned the correct values.

Upvotes: 0

Views: 657

Answers (2)

Seth Carnegie
Seth Carnegie

Reputation: 75150

Your constructor is marked CLimb(CLimb *_parent); meaning it takes a pointer to a CLimb but in the CNeck constructor,

CNeck::CNeck(CLimb *_parent) : CLimb(*_parent)

you're dereferencing the pointer, which calls CLimb(CLimb&) which is the copy constructor. Turn *_parent into _parent to resolve this problem. Plus you might want to define a copy constructor as well.

In other news, don't do this:

CLimb *ptr;
ptr = &hand;

Do this:

CLimb *ptr = &hand;

To avoid wasting cycles.

And you also don't need void in the parameter list for functions which take no parameters (that's the way C does it, not C++). So for example:

CLimb(void);
CLimb(CLimb *_parent);
~CLimb(void);

Should be

CLimb();
CLimb(CLimb *_parent);
~CLimb();

I know it's not related to your question, but it's good style.

Upvotes: 1

Alok Save
Alok Save

Reputation: 206646

CNeck::CNeck(CLimb *_parent) : CLimb(*_parent)

should be

CNeck::CNeck(CLimb *_parent) : CLimb(_parent)

Besides, I don't really understand how this compiled:

ptr = &hand;

hand is not declared at all, but looks like you missed it while copy pasting the code here.

Upvotes: 2

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