add x hours to sunset

[Jay Ess 6]

Hi

I am trying to add 5 hours to sunset and then use that time as an off time for some lights, am using the following code:

local fmt = string.format

function str2sec(str) local h,m,s=str:match("^(%d%d):(%d%d):?(%d*)") return 3600*h+60*m+(s~="" and s or 0) end

function sec2str(sec) return fmt("%02d:%02d%s",math.floor(sec/3600),math.floor((sec % 3600)/60),sec % 60 > 0 and fmt(":%02d",sec%60) or "") end

local SunSetTimeVariable = fibaro.getGlobalVariable("Sunset") --this is a stored value of sunset time updated every day.

local LightOffTime = sec2str(str2sec(SunSetTimeVariable)+(300*60))

 

when I debug this I get:

sunset 20:41

LightOffTime 25:41

 

This seems to be an error as there is no such time as 25 hours?

 

Can someone please help me where I have gone wrong please?

[jgab 2,642]

5 hours ago, Jay Ess said:

Hi

I am trying to add 5 hours to sunset and then use that time as an off time for some lights, am using the following code:

local fmt = string.format

function str2sec(str) local h,m,s=str:match("^(%d%d):(%d%d):?(%d*)") return 3600*h+60*m+(s~="" and s or 0) end

function sec2str(sec) return fmt("%02d:%02d%s",math.floor(sec/3600),math.floor((sec % 3600)/60),sec % 60 > 0 and fmt(":%02d",sec%60) or "") end

local SunSetTimeVariable = fibaro.getGlobalVariable("Sunset") --this is a stored value of sunset time updated every day.

local LightOffTime = sec2str(str2sec(SunSetTimeVariable)+(300*60))

 

when I debug this I get:

sunset 20:41

LightOffTime 25:41

 

This seems to be an error as there is no such time as 25 hours?

 

Can someone please help me where I have gone wrong please?

If you are adding time you need to make sure you don't spill over 24 hours. Take the seconds modulo 24*3600 (seconds in 24 hours) and you get the rest.

local LightOffTime = sec2str((str2sec(SunSetTimeVariable)+(300*60)) % (24*60*60))

[Jay Ess 6]

@jgab

Thank you for your help, it works a treat. Can you explain what the % is doing please?

[jgab 2,642]

1 hour ago, Jay Ess said:

@jgab

Thank you for your help, it works a treat. Can you explain what the % is doing please?

% is called the 'Modulus Operator' and is the remainder after an integer division.

26 % 24 => 2

and that is what we use to make sure that if the time exceeds 24hours we wrap around.

% also has the nice property that 

20 % 24 => 20

so we can use it even when the time is less than 24 hour

[jgab 2,642]

...and it's quite useful

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will print
 

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Adding one makes it give the sequence 1,2,3,4,1,2,3,4 

because % binds harder than + so i%4+1 == (I%4)+1

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Assume you want to take the next in an array and make the index wrap around

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[Jay Ess 6]

@jgab

Thank you for your help.

[jgab 2,642]

If you code a QA and do a lot of time manipulation you could add this 24hour time type

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Edited May 3, 2021 by jgab