Objective-C - Get number of decimals of a double v

问题:

Is there a nice way to get the number of decimals of a double variable in Objective-C? I am struggling for a while to find a way but with no success.

For example 231.44232000 should return 5.

Thanks in advance.

回答1:

You could, in a loop, multiply by 10 until the fractional part (returned by modf()) is really close to zero. The number of iterations'll be the answer you're after. Something like:

int countDigits(double num) {
  int rv = 0;
  const double insignificantDigit = 8;
  double intpart, fracpart;
  fracpart = modf(num, &intpart);
  while ((fabs(fracpart) > 0.000000001f) && (rv < insignificantDigit)) {
    num *= 10;
    rv++;
    fracpart = modf(num, &intpart);
  }

  return rv;
}

回答2:

Is there a nice way to get the number of decimals of a double variable in Objective-C?

No. For starters, a double stores a number in binary, so there may not even be an exact binary representation that corresponds to your decimal number. There's also no consideration for the number of significant decimal digits -- if that's important, you'll need to track it separately.

You might want to look into using NSDecimalNumber if you need to store an exact representation of a decimal number. You could create your own subclass and add the ability to store and track significant digits.