Re: Sign of a number ...

From:

"Victor Bazarov" <v.Abazarov@comAcast.net>

Newsgroups:

comp.lang.c++

Date:

Wed, 14 Nov 2007 11:51:55 -0500

Message-ID:

<fhf93d$2gj$1@news.datemas.de>

mathieu wrote:

On Nov 14, 4:14 pm, "Victor Bazarov" <v.Abaza...@comAcast.net> wrote:

Konrad MLhler wrote:

a simple question:

Which standard function in c++ gives me the sign of a number?

There is no standard function in C++ (mostly because there is no
agreement on what such function would return for 0, for example).
Why do you ask? Is it difficult to write? Are you concerned
with performance?

You can do it with bits field:

Why are you replying to me? If I were to do it, I'd simply write

    template<class T> int sign(T t) {
        return t < 0 ? -1 : t > 0 ? 1 : 0;
    }

but that's just one definition of 'sign' (another treats 0 as
a positive value). Besides, the OP may want to return T instead
of 'int'...

#include <iostream>

template <typename T>
struct Sign
{
bool S:1;
T Remaining:(sizeof(T)-1);

'sizeof' does NOT return the number of bits in the object...

};

int main()
{
  Sign<int> z;
  int zero = 0;
  int minusone = -1;
  float minuszero = -0.0;
  memcpy(&z,&zero,sizeof(zero));
  std::cout << z.S << std::endl;
  memcpy(&z,&minusone,sizeof(minusone));
  std::cout << z.S << std::endl;

  Sign<int> zz;
  memcpy(&zz,&minuszero,sizeof(minuszero));
  std::cout << z.S << std::endl;
  return 0;
}

In which case 0 and -0 are different, this will not be compatible with
a solution using '<' and/or '>'

HTH

'fraid it don't. Have you actually tested your program before posting?

-Mathieu

V
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