working dtostrf

[jsmith]

I needed a *working* dtostrf and since I could not find one I am contributing one with example.

-------<SNIP>--------

#include <stdlib.h>

float x = 0.0;
float y = 0.0;

char *dtostrf(double value, int width, unsigned int precision, char *result)
{
  int decpt, sign, reqd, pad;
  const char *s, *e;
  char *p;
  s = fcvt(value, precision, &decpt, &sign);
  if (precision == 0 && decpt == 0) {
  s = (*s < '5') ? "0" : "1";
    reqd = 1;
  } else {
    reqd = strlen(s);
    if (reqd > decpt) reqd++;
    if (decpt == 0) reqd++;
  }
  if (sign) reqd++;
  p = result;
  e = p + reqd;
  pad = width - reqd;
  if (pad > 0) {
    e += pad;
    while (pad-- > 0) *p++ = ' ';
  }
  if (sign) *p++ = '-';
  if (decpt <= 0 && precision > 0) {
    *p++ = '0';
    *p++ = '.';
    e++;
    while ( decpt < 0 ) {
      decpt++;
      *p++ = '0';
    }
  }   
  while (p < e) {
    *p++ = *s++;
    if (p == e) break;
    if (--decpt == 0) *p++ = '.';
  }
  if (width < 0) {
    pad = (reqd + width) * -1;
    while (pad-- > 0) *p++ = ' ';
  }
  *p = 0;
  return result;
}

void setup() {
  while( !SerialUSB ) ;
  Serial.begin(9600);
}

void loop() {
  char str1[20];
  char str2[20];
  x += 0.001;
  y -= 0.001;
  dtostrf(x, 6, 3, str1);
  dtostrf(y, 6, 3, str2);
  SerialUSB.print( "X Val:" );
  SerialUSB.print( str1 );
  SerialUSB.print( " Y Val:" );
  SerialUSB.println( str2 );
}

[jsmith]

Update:

Edit your dtostrf.c to look like the following. It fixes LOTS of bugs in the current libraries.

----<SNIP>----

/*
  dtostrf - Emulation for dtostrf function from avr-libc
  Copyright (c) 2015 Arduino LLC.  All rights reserved.

  This library is free software; you can redistribute it and/or
  modify it under the terms of the GNU Lesser General Public
  License as published by the Free Software Foundation; either
  version 2.1 of the License, or (at your option) any later version.

  This library is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General Public
  License along with this library; if not, write to the Free Software
  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
*/

#include <stdio.h>

#if 0
char *dtostrf (double val, signed char width, unsigned char prec, char *sout) {
  char fmt[20];
  sprintf(fmt, "%%%d.%df", width, prec);
  sprintf(sout, fmt, val);
  return sout;
}
#else
#include <string.h>
#include <stdlib.h>
char *dtostrf(double val, int width, unsigned int prec, char *sout)
{
  int decpt, sign, reqd, pad;
  const char *s, *e;
  char *p;
  s = fcvt(val, prec, &decpt, &sign);
  if (prec == 0 && decpt == 0) {
  s = (*s < '5') ? "0" : "1";
    reqd = 1;
  } else {
    reqd = strlen(s);
    if (reqd > decpt) reqd++;
    if (decpt == 0) reqd++;
  }
  if (sign) reqd++;
  p = sout;
  e = p + reqd;
  pad = width - reqd;
  if (pad > 0) {
    e += pad;
    while (pad-- > 0) *p++ = ' ';
  }
  if (sign) *p++ = '-';
  if (decpt <= 0 && prec > 0) {
    *p++ = '0';
    *p++ = '.';
    e++;
    while ( decpt < 0 ) {
      decpt++;
      *p++ = '0';
    }
  }   
  while (p < e) {
    *p++ = *s++;
    if (p == e) break;
    if (--decpt == 0) *p++ = '.';
  }
  if (width < 0) {
    pad = (reqd + width) * -1;
    while (pad-- > 0) *p++ = ' ';
  }
  *p = 0;
  return sout;
}
#endif

[david_prentice]

Please edit your code so that it lies within code tags.

Note that SAM code links with full-fat printf() family.    So there is no need to use the non-standard dtostrf except for compatibility with the small AVR.

David.

[pjrc]

When I see this line:

there is no need to use the non-standard dtostrf except for compatibility with the small AVR.

what I see is...

there is no need ... for compatibility with the small AVR.

Perhaps it wasn't meant this way?

[roadfun]

smith - thanks for posting this, exactly what I needed on my Feather M0.

[machman2823]

I'm wondering how to use this in a sketch. Do I have to make it into a library? if so, how would I do that?

It would be used to display temperature and humidity data with a feather M0 and Adafruit's quad alphanumeric display wing. any help would be great.

[dgreenblaze]

Hi, I'd like to follow-on with machman2823's question on use of the sketch.  Is it to be added as a library file (*.h)?  My project is to capture and transmit data from an Electret microphone to the receiver module which will trigger a hobby servo. 

Please help, as I'm also a "newbie" level hack!

Cheers