question on function overloading
raksha
I have a class A which is the base class. I have class B which is
derived class of A.
Class A does not have a default constructor(reason it is a class in c+
+ library).
I am trying to overload a function of class A in class B and it gives
me an error saying there is no appropriate default constructor
available. Is there any way to solve this problem?
Thanks
Raksha
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red floyd
> Hi,
>
> I have a class A which is the base class. I have class B which is
> derived class of A.
> Class A does not have a default constructor(reason it is a class in c+
> + library).
> I am trying to overload a function of class A in class B and it gives
> me an error saying there is no appropriate default constructor
> available. Is there any way to solve this problem?
You have an error on line 42 of your code. Please post a minimum,
compilable example that exhibits the behavior in question.
Kacper Gazda
material (greetings, signature, banner, etc.) from your quoting. -mod }
On 12 Lis, 02:18, raksha <raksha...@gmail.com> wrote:
> Hi,
>
> I have a class A which is the base class. I have class B which is
> derived class of A.
> Class A does not have a default constructor(reason it is a class in c+
> + library).
> I am trying to overload a function of class A in class B and it gives
> me an error saying there is no appropriate default constructor
> available. Is there any way to solve this problem?
>
> Thanks
> Raksha
>
> --
> [ Seehttp://www.gotw.ca/resources/clcm.htmfor info about ]
> [ comp.lang.c++.moderated. First time posters: Do this! ]
Could you paste your class A and B implementation( showing the
problematic method)???
This could help me to solve your problem and identify the operation
that required the default constructor in A.
Thanks,
Kacper
Gerhard Menzl
> I have a class A which is the base class. I have class B which is
> derived class of A.
> Class A does not have a default constructor(reason it is a class in
> c++ library).
> I am trying to overload a function of class A in class B and it gives
> me an error saying there is no appropriate default constructor
> available. Is there any way to solve this problem?
There sure is. Its first step is to post stripped down, minimal, and
compilable code that exposes the problem.
Terminological hint: you cannot overload a member function of a class in
a class dervied from it. This would be overriding (if it is a virtual
function) or hiding (if it isn't)
--
Gerhard Menzl
Non-spammers may respond to my email address, which is composed of my
full name, separated by a dot, followed by at, followed by "fwz",
followed by a dot, followed by "aero".
Goran
> Hi,
>
> I have a class A which is the base class. I have class B which is
> derived class of A.
> Class A does not have a default constructor(reason it is a class in c+
> + library).
> I am trying to overload a function of class A in class B and it gives
> me an error saying there is no appropriate default constructor
> available. Is there any way to solve this problem?
class B : public A
{
public:
B() : A(whatever params A::A needs) {}
};
IOW: you must call appropriate constructor of A in whatever
constructor B might have. That must be the case happens even if A has
a default constructor, but then you don't have to spell it out,
compiler does it.
Goran.
raksha
here is an example...
class A // defined in the library...which i cant edit it
{
//no default constructor defined like A(){}
//there are other constructors with input arguments define like
A(int i) { };
//function in this class
int wait()
{
//do something
}
}
//header file of class B
class B: public A
{
public:
//overload the wait function
using A::wait;
int wait(int tokens);
}
//cpp file of class B
int B::wait(int tokens)
{
//do something different from other wait function
}
In the above example...since class A doesnt have a default constructor
it gives me an error saying default construtor not available...how can
i solve this
Raksha
dietma...@gmail.com
> I have a class A which is the base class. I have class B which is
> derived class of A.
> Class A does not have a default constructor(reason it is a class in c+
> + library).
> I am trying to overload a function of class A in class B and it gives
> me an error saying there is no appropriate default constructor
> available. Is there any way to solve this problem?
I don't think your problem is with overloading! The problem rather
seems to be that you don't know how to initialize a base class which
doesn't have a default constructor. This is simply done using a member
initializer list:
struct A { A(long); /* other members */ };
struct B: A
{
B(int);
private:
A m_value;
};
B::B(int value): // colon indicates start of member initializer list
A(value), // pass a value to the base class constructor
m_value(value) // pass a value to a data member's constructor
{
Kacper Gazda
> [ comp.lang.c++.moderated. First time posters: Do this! ]
Thank you for this minimum compilable example.
There is few questions I would like to ask according to the code you
have pasted:
1) why are You using the "using A::wait" in the B class body?
2) You would like to overload the the B's wait with A's wait?
3) All methods/data in class A are private??
Here is a sample of code which works, but I am not sure what you
really need and
what do you want to achieve.
Could you explain why are you designing the A,B classes the way you
showed ?
#include <iostream>
using namespace std;
class A
{
public:
A(int i) {cout<<"A ctor with value->"<<i<<"\n";}
int wait() { cout<<"I am in A::wait\n";}
};
class B: public A
{
public:
B(int i):A(i) { cout<<"B ctor with value->"<<i<<"\n";}
using A::wait;
int wait(int tokens) {cout<<"I am in B::wait,value->"<<tokens<<"\n";}
};
int main(int argc, char** argv)
{
A a(10);
a.wait();
B b(11);
b.wait();
return 0;
}
If you explain your design and give as much information as possible I
am sure we can help you
with your problem. But first justify your design and please explain
what do you want to achieve.
Thanks,
Kacper
red floyd
> okay
>
> here is an example...
>
> class A // defined in the library...which i cant edit it
> {
>
> //no default constructor defined like A(){}
> //there are other constructors with input arguments define like
> A(int i) { };
>
> //function in this class
> int wait()
> {
> //do something
>
> }
> }
>
> //header file of class B
> class B: public A
> {
> public:
>
> //overload the wait function
> using A::wait;
> int wait(int tokens);
>
> }
>
> //cpp file of class B
> int B::wait(int tokens)
> {
> //do something different from other wait function
>
> }
>
> In the above example...since class A doesnt have a default constructor
> it gives me an error saying default construtor not available...how can
> i solve this
You problem has absolutely nothing to do with the overload of wait().
It has to do with the fact that since B is derived from A, and you
provide no constructor
for B, it uses A's default constructor... which doesn't exist.
You need a B constructor that constructs the A portion using A::A
(int).