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Using printf to output hexadecimal

 
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pl7



Joined: 15 Mar 2007
Posts: 2
Location: UK

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Using printf to output hexadecimal
PostPosted: Thu Apr 30, 2009 7:55 am     Reply with quote
Hi,

An easy question, I hope. I'm puzzled by the behaviour of printf on a PIC 18F452.

Code:

int8 a;

a = 1;
printf("%d", a);


produces 1, but

Code:

int8 a;

a = 1;
printf("%x", a);


produces 01.

This seems to be incorrect to me. I expected a single hex character for values of a < 16. Is the extra zero a CCS "feature"? Does anyone know how to achieve a single character using the printf format specification?

Thanks,

Phil
treitmey



Joined: 23 Jan 2004
Posts: 1094
Location: Appleton,WI USA

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PostPosted: Thu Apr 30, 2009 8:37 am     Reply with quote
If your just trying to print a 1 thats easy.
Do it via printing the character.
The character 1 is ascii 49.
So to change 0x01 to 0x31 you add 0x30.
The more common way is to add '0'
Code:
#include <18F4620.h>
#fuses hs,nowdt,noprotect,nolvp,put
#use delay(clock=18432000,RESTART_WDT)
#use rs232(baud=19200,xmit=PIN_E0,invert,stream=DEBUG)
#use rs232(baud=1200,errors,xmit=PIN_C6,rcv=PIN_C7,parity=e,enable=PIN_C5,bits=8,stream=CIM)
#case
void main()
{
  int8 k=1;
  k=k+'0';
  //fprintf(DEBUG,"%X\n\r",k);
  fprintf(DEBUG,"%C\n\r",k);
  while (1)
  {
  }
}

FvM



Joined: 27 Aug 2008
Posts: 2337
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PostPosted: Thu Apr 30, 2009 9:13 am     Reply with quote
Use standard a format string (%x seems to default to %02x):
Quote:
printf("%1x", a);
pl7



Joined: 15 Mar 2007
Posts: 2
Location: UK

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PostPosted: Thu Apr 30, 2009 9:30 am     Reply with quote
FvM wrote:
Use standard a format string (%x seems to default to %02x):
Quote:
printf("%1x", a);


This was my first thought too, but the width part of the format string specifies a minimum number of digits, not a maximum, so it seems strange to specify a minimum width when really I want to shorten the output. However, I'm sure you are right: CCS is simply substituting %02x for %x, so your solution will work.

Sorry, I would normally have just tried this myself but I have no access to any hardware at the moment.

Thanks for the input,

Phil
Ttelmah
Guest
PostPosted: Thu Apr 30, 2009 9:35 am     Reply with quote
I suspect the 'reason', is quite logical, when you think that a int8, is inherently two hex digits.
Just another CCS oddity. Smile

Best Wishes
FvM



Joined: 27 Aug 2008
Posts: 2337
Location: Germany

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PostPosted: Thu Apr 30, 2009 1:18 pm     Reply with quote
Quote:
Sorry, I would normally have just tried this myself but I have no access to any hardware at the moment.
You don't actually need it. I was using MPLAB SIM, cause I didn't want to re-flash a board for this trivial test.
Quote:
Just another CCS oddity.
Yes. I'm satisfied so far, if CCS C understands standard format specifiers, which is the case, fortunately.
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