Retrieve the decimal part of a double

Question

Possible Duplicate:
Extract decimal part from a floating point number in C

I would like retrieve the decimal part of a double in the most efficient way.

Something like this:

double a = 1.5;
double decimal_part = a -1 ; // decimal_part = 0.5

How retrieve and store in a variable in a really efficient way the .5 (decimal part of a) ?

How do you want to deal with negative values? – David Heffernan Jan 27 '12 at 09:39 — David Heffernan, Jan 27 '12 at 09:39

score 5 · Accepted Answer · answered Jan 27 '12 at 09:31

5

Use modf function:

double integer_part;
double decimal_part = modf(a, &integer_part);

answered Jan 27 '12 at 09:31

Vladimir

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The pointer supplied to `modf()` is not allowed to be `NULL`. – caf Jan 27 '12 at 09:33

ouah · Answer 2 · 2012-01-27T09:39:58.437

1

Use modf function from math.h for double and modff for float.

#include <math.h>

double val = 3.14159;
double integral_part;
double fractional_part;

/*
 * integral_part will be 3.0
 * fractional_part will be 0.14159
 */
fractional_part = modf(val, &integral_part);

edited Jan 27 '12 at 09:39

answered Jan 27 '12 at 09:34

ouah

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score 0 · Answer 3 · answered Jan 27 '12 at 09:32

0

double a = 5.6;
double f = a - int(a); // int(a) chops off fraction

you have to make sure ranges are sane st int doesn't overflow.

answered Jan 27 '12 at 09:32

Anycorn

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Not safe, the int conversion can overflow. – Mat Jan 27 '12 at 09:34

Retrieve the decimal part of a double

3 Answers3