Question about sprintf and float variables

ccdart · Joined: 12 Jan 2005 Posts: 3 Location: Seattle, WA, USA

Here is a short test program:

// fuses, etc. not shown
void main(void)
{
signed int8 c=100;
float value=0;
char ascout[20];

value = (float)c;

sprintf(ascout,"%f",value);
}

Now, I'm using MPLAB 7.00 with CCS as the designated tool suite. The CCS version (IDE/PCB/PCM) is 3.215

When I run the above program in the MPLAB simulator and examine the variable contents afterwards, I see:

c = 0x64 (as expected)
value = "100.0000" which, read from memory, is 0x85, 0x48, 0x00, 0x00 (again as expected)
BUT:
ascout contains "99.999999" (!) [followed by terminating 0x00, as expected].

If I change the sprintf specification to "%3.0f", ascout is then "99". If, instead, I use "%3.1f", ascout then contains "99.9".

I tried adding this line: value = value + 0.000001; before the sprintf. Now I get the (predictable, at least) result of "100.000001". Grrr...

It appears to me as if the conversion from signed int8 to float is working okay, but sprintf is not. Of course, what I want is an ascii string of "100.000000"

What must I do to get this result?
TIA

Ttelmah · Guest

ccdart · Joined: 12 Jan 2005 Posts: 3 Location: Seattle, WA, USA

Okay, that's pretty much what I was expecting to hear. I'll try your suggestion ASAP... if true, it should be good enough.

ccdart · Joined: 12 Jan 2005 Posts: 3 Location: Seattle, WA, USA

Yup! That does it. I also tried four decimal places and adding .000049, and that seems to work as well. (Though I wonder if that's treading on thin ice...)

Thanks again for the solution!