The most effective way to format numbers on Arduino

If "effective way" is minimum effort you could hack the avr-libc source code for ltoa and do something like below:

char *ultos_recursive(unsigned long val, char *s, unsigned radix, int pos)
{
  int c;

  if (val >= radix)
    s = ultos_recursive(val / radix, s, radix, pos+1);
  c = val % radix;
  c += (c < 10 ? '0' : 'a' - 10);
  *s++ = c;
  if (pos % 3 == 0) *s++ = ',';
  return s;
}

char *ltos(long val, char *s, int radix)
{
  if (radix < 2 || radix > 36) {
    s[0] = 0;
  } else {
    char *p = s;
    if (radix == 10 && val < 0) {
      val = -val;
      *p++ = '-';
    }
    p = ultos_recursive(val, p, radix, 0) - 1;
    *p = 0;
  }
  return s;
}

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

  char buf[32];
  Serial.println(ltos(12345678, buf, 10));
  Serial.println(ltos(-12345678, buf, 10));
}

void loop()
{
}

Gives the output:

12,345,678
-12,345,678

Cheers!

PS: Please see the table driven, non-recursive, number conversion in Cosa (source and benchmark) for lean and fast implementation.

The most effective way to format numbers on Arduino

If "effective way" is minimum effort you could hack the avr-libc source code for ltoa and do something like below:

char *ultos_recursive(unsigned long val, char *s, unsigned radix, int pos)
{
  int c;

  if (val >= radix)
    s = ultos_recursive(val / radix, s, radix, pos+1);
  c = val % radix;
  c += (c < 10 ? '0' : 'a' - 10);
  *s++ = c;
  if (pos % 3 == 0) *s++ = ',';
  return s;
}

char *ltos(long val, char *s, int radix)
{
  if (radix < 2 || radix > 36) {
    s[0] = 0;
  } else {
    char *p = s;
    if (radix == 10 && val < 0) {
      val = -val;
      *p++ = '-';
    }
    p = ultos_recursive(val, p, radix, 0) - 1;
    *p = 0;
  }
  return s;
}

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

  char buf[32];
  Serial.println(ltos(12345678, buf, 10));
  Serial.println(ltos(-12345678, buf, 10));
}

void loop()
{
}

Gives the output:

12,345,678
-12,345,678

Cheers!

PS: Please see the table driven, non-recursive, number conversion in Cosa (source and benchmark) for a lean and faster implementation.

The most effective way to format numbers on Arduino

If "effective way" is minimum effort you could hack the avr-libc source code for ltoa and do something like below:

char *ultos_recursive(unsigned long val, char *s, unsigned radix, int pos)
{
  int c;

  if (val >= radix)
    s = ultos_recursive(val / radix, s, radix, pos+1);
  c = val % radix;
  c += (c < 10 ? '0' : 'a' - 10);
  *s++ = c;
  if (pos % 3 == 0) *s++ = ',';
  return s;
}

char *ltos(long val, char *s, int radix)
{
  if (radix < 2 || radix > 36) {
    s[0] = 0;
  } else {
    char *p = s;
    if (radix == 10 && val < 0) {
      val = -val;
      *p++ = '-';
    }
    p = ultos_recursive(val, p, radix, 0) - 1;
    *p = 0;
  }
  return s;
}

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

  char buf[32];
  Serial.println(ltos(12345678, buf, 10));
  Serial.println(ltos(-12345678, buf, 10));
}

void loop()
{
}

Gives the output:

12,345,678
-12,345,678

Cheers!

The most effective way to format numbers on Arduino

If "effective way" is minimum effort you could hack the avr-libc source code for ltoa and do something like below:

char *ultos_recursive(unsigned long val, char *s, unsigned radix, int pos)
{
  int c;

  if (val >= radix)
    s = ultos_recursive(val / radix, s, radix, pos+1);
  c = val % radix;
  c += (c < 10 ? '0' : 'a' - 10);
  *s++ = c;
  if (pos % 3 == 0) *s++ = ',';
  return s;
}

char *ltos(long val, char *s, int radix)
{
  if (radix < 2 || radix > 36) {
    s[0] = 0;
  } else {
    char *p = s;
    if (radix == 10 && val < 0) {
      val = -val;
      *p++ = '-';
    }
    p = ultos_recursive(val, p, radix, 0) - 1;
    *p = 0;
  }
  return s;
}

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

  char buf[32];
  Serial.println(ltos(12345678, buf, 10));
  Serial.println(ltos(-12345678, buf, 10));
}

void loop()
{
}

Gives the output:

12,345,678
-12,345,678

Cheers!

PS: Please see the table driven, non-recursive, number conversion in Cosa (source and benchmark) for lean and fast implementation.