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Double precision and iostream library

Posted on 1997-02-26
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Last Modified: 2008-02-26
Hi,

the following problem:

I have a double precision number,
double x = -9.3456

Then I try to output it using the following commands:
cout.setf(ios::fixed,ios::floatfield);
cout.precision(16);
cout << x;

...and this is the result:

-9.3455999999999992

What I need to know is:

which is the number actualy stored in memory ?
what happens ?

Thanks for any help.

Roberto

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Question by:roberto022697
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Accepted Solution

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jordan122196 earned 200 total points
ID: 1162124
The actual number stored in memory is:
-9.3455999999999992

This is the closest number to -9.3456 that can be stored
in the bits of a double.  Numbers are stored in base 2 (one's
and zeros).  Thus you can exactly store the numbers: 8,4,0.5,
0.25, etc. but a number like 0.1 cannot be exactly stored.

In computer science we accept this small error ( called floating
point error ) as a fact of life.

jordan

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