# Cookbook/Dates And Time

From HaskellWiki

## Contents

## Finding today's date

```
import Data.Time
c <- getCurrentTime --> 2009-04-21 14:25:29.5585588 UTC
(y,m,d) = toGregorian $ utctDay c --> (2009,4,21)
```

## Adding to or subtracting from a date

Problem | Solution | Examples |
---|---|---|

adding days to a date | addDays | ```
import Data.Time
a = fromGregorian 2009 12 31 --> 2009-12-31
b = addDays 1 a --> 2010-01-01
``` |

subtracting days from a date | addDays | ```
import Data.Time
a = fromGregorian 2009 12 31 --> 2009-12-31
b = addDays (-7) a --> 2009-12-24
``` |

## Difference of two dates

Problem | Solution | Examples |
---|---|---|

calculating the difference of two dates | diffDays | ```
import Data.Time
a = fromGregorian 2009 12 31 --> 2009-12-31
b = fromGregorian 2010 12 31 --> 2010-12-31
diffDays b a --> 365
``` |

## CPU time

Use System.CPUTime.getCPUTime to get the CPU time in picoseconds.

You can time a computation like this

```
getCPUTimeDouble :: IO Double
getCPUTimeDouble = do t <- System.CPUTime.getCPUTime; return ((fromInteger t) * 1e-12)
main = do
t1 <- getCPUTimeDouble
print (fib 30)
t2 <- getCPUTimeDouble
print (t2-t1)
```