Re: calling virtual function from within another virtual function

From:

terminator <farid.mehrabi@gmail.com>

Newsgroups:

comp.lang.c++.moderated

Date:

Sun, 8 Feb 2009 14:04:22 CST

Message-ID:

<b56aacc7-8070-4dac-a81d-180c52a88cab@o11g2000yql.googlegroups.com>

On Feb 6, 12:25 pm, srp113 <sunilsreenivas2...@yahoo.com> wrote:

Hi Guys,
Is Ok to invoke a virutal function from within virtual function.
Specifically here is the example I tried and it seems to have worked:
(what I am doing is derived class::foo() (foo is virtual)invokes base
case implementation of foo(), which in turn calls bar() thats virutal
too . So I am reusing some part of logic which is common to both base
and derived and overriding other part which is different by using 2
virtual functions like this)

#include <iostream.h>
using namespace std;

class C {
public:
virtual void foo(int foo) {

bad idea. I do not use same names for functions and variables(I am not
sure if this should compile).In either case this voilates readability
of your program.

cout << "in C::foo() foo=" << foo << endl;
bar(foo);
}

virtual void bar(int bar) {

same as above

cout << "in C::bar() bar=" << bar << endl;
}
private:
int i;

};

class A : public C {
public:
virtual void foo(int foo) {

again

cout << "in A::foo() foo=" << foo << endl;
if(foo > 0)
C::foo(foo);
}

virtual void bar(int bar) {

and again.

cout << "in A::bar() bar=" << bar << endl;
}

};

int main()
{
C c;
A a;

c.foo(10);
a.foo(20);

C* tmp;
tmp = &c;
tmp->foo(30);
tmp = &a;
tmp->foo(40);

}

output:
in C::foo() foo=10
in C::bar() bar=10

in A::foo() foo
in C::foo() foo
in A::bar() bar

in C::foo() foo=30
in C::bar() bar=30

in A::foo() foo=40
in C::foo() foo=40
in A::bar() bar=40

so is it OK to use polymorphism like this from point of view of C++
standard? I tried this with SUN CC compiler on a solaris box. Are
there any potential downsides to following this paradigm, if so what
would be better way of doing this?
Thanks,
Sunil

I do not know what you want to do ,but the standard behavoir is just
what you have seen.Virtual functions are called polymorphycally (via
ref/ptr variables) unless prefixed by class name.

regards,
FM.

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