g++/gcc : Floating point issue

[miridian]

abuzer.salik@tcs.com wrote:

> I have an application which uses double values a lot. If I try to put say
> 401.74 in a double variable it is getting stored as 401.74000000000001
> which creates problem in the calculations down the line. ( I am checking
> these values using gdb debugger).
> 
> So, I am wondering if there is a way by which I can store the correct
> values (i.e. 401.74) in the double.

No.

Only dyadic rationals (a rational number of the form a/(2^b) where a is 
an integer and b is a natural number) have a finite binary expansion.

   40174/100 = 200087/50    (and 50 is not 2^b for a natural number b)

See the links:
http://en.wikipedia.org/wiki/Binary_numeral_system#Representing_real_numbers
http://en.wikipedia.org/wiki/Dyadic_fraction


> Do we need to look for another compiler/hardware or current setup can
> handle this?

You can use an arbitrary precision numeric library, for ex. GMP
  http://www.swox.com/gmp/

Regars,
Luca.