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Printf formatting....

 
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JAM2014



Joined: 24 Apr 2014
Posts: 129

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Printf formatting....
PostPosted: Wed Jun 23, 2021 2:51 pm     Reply with quote

Hi All,

I have an signed int8 variable that varies from -10 to +10. I'd like to display the value exactly this way using the printf function. Is there a format specifier that will allow me to do this in a single line? Currently, I need to do this in two lines depending on whether the value is less than 0 or not.
Code:

if (UTCOffset < 0){
               sprintf(TempTimeStr,"PageSetup.txtUTCOffset.txt=\"%03d\"", UTCOffset); SendNextionValue(TempTimeStr);
            }
            else{
               sprintf(TempTimeStr,"PageSetup.txtUTCOffset.txt=\"+%02d\"", UTCOffset); SendNextionValue(TempTimeStr);
         }


This is not a huge deal except I have other similar variables that I'd like to do in the same way, and the code is getting a bit 'messy'!

Edit: Changed description of variable type!

Thanks,

Jack


Last edited by JAM2014 on Wed Jun 23, 2021 5:51 pm; edited 1 time in total
temtronic



Joined: 01 Jul 2010
Posts: 8181
Location: Greensville,Ontario

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PostPosted: Wed Jun 23, 2021 5:24 pm     Reply with quote

hmmm...
Quote:
I have an unsigned int8 variable that varies from -10 to +10.

me thinks you have a SIGNED int8 variable...
Ttelmah



Joined: 11 Mar 2010
Posts: 17398

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PostPosted: Wed Jun 23, 2021 11:55 pm     Reply with quote

Yes.
However the problem he is having is down to CCS missing one of the standard
C format flags.
By default a number displays a leading - if negative, but nothing if positive.
There was a flag defined in K&R, that + could be used in front of the
width specifier, and if this existed, the formatter would display + if positive
and - if negative. This though is not supported in CCS. Sad

Suggestion. Create a function to do it. So:
Code:

char * string_with_sign(signed int8 val)
{
   static char buffer[4]; //remember need to be space for NULL as well
   //also must be static so can be returned
   if (val< 0)
   {
        sprintf(buffer,"%03d", val);
   }
   else
   {
        sprintf(buffer,"+%02d", val);
   } 
   return buffer;
}

//Then when you want to print the value, use this and %s
   sprintf(TempTimeStr,"PageSetup.txtUTCOffset.txt=\"%s\"", string_with_sign(UTCOffset)); SendNextionValue(TempTimeStr);


Now this can then be used for other values. It just generates a 3 character
'string' containing the number formatted as required.
JAM2014



Joined: 24 Apr 2014
Posts: 129

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PostPosted: Fri Jun 25, 2021 7:42 am     Reply with quote

Hi All,

Temtronic: Thanks for pointing out the error in my OP!

Ttelmah: That is perfect! Exactly the idea I was looking for!

Thanks,

Jack
Ttelmah



Joined: 11 Mar 2010
Posts: 17398

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PostPosted: Fri Jun 25, 2021 8:02 am     Reply with quote

I've actually suggested to CCS, that they might want to consider adding the flags. There are two. + for leading plus, and - for left justify in the output
field. They are C features that at time can be useful.
I knew exactly what you were saying, since I had found this myself some
time ago.... Sad
JAM2014



Joined: 24 Apr 2014
Posts: 129

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PostPosted: Fri Jun 25, 2021 11:26 am     Reply with quote

Hi All,

As a quick follow-up, a CCS fix would be nice, but in the meantime....

I was thinking that a more universal fix might be desirable that could accommodate different width variables. At the moment, I have both -10 to +10, and -125 to +125, so I currently need at least two formats. I have passed a 'count' variable to the new function, and handle things differently depending on a count of '2' or a count of '3', but it would be nice to have something more flexible. I haven't found a way to make the format specifier, eg. "+%02d", use a variable. How could that be done neatly/cleanly?

Thanks,

Jack
jeremiah



Joined: 20 Jul 2010
Posts: 1226

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PostPosted: Fri Jun 25, 2021 1:16 pm     Reply with quote

JAM2014 just make sure not to use that function in other code without ensuring that the values are between -99 and +99 or it will overwrite memory. Once the values hit 3 digits your string variable inside the function needs to be at least a size 5 (currently a size 4) to hold the 1 digit sign, a 3 digit number, and the null character.

You could adjust it to be a 5 byte string and then you can use it universally.
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