Find number of decimal places in decimal value regardless of culture

Question

I m wondering if there is a concise and accurate way to pull out the number of decimal places in a decimal value  as an int  that will be safe to use across different culture info   For example  19 0 should return 1  27 5999 should return 4  19 12 should return 2  etc   I wrote a query that did a string split on a period to find decimal places   int priceDecimalPlaces   price ToString   Split      Count    gt  1                      price ToString   Split      ToList   ElementAt 1  Length                      0    But it occurs to me that this will only work in regions that use the     as a decimal separator and is therefore very brittle across different systems

User · Answer

Most people here seem to be unaware that decimal considers trailing zeroes as significant for storage and printing.

So 0.1m, 0.10m and 0.100m may compare as equal, they are stored differently (as value/scale 1/1, 10/2 and 100/3, respectively), and will be printed as 0.1, 0.10 and 0.100, respectively, by ToString().

As such, the solutions that report "too high a precision" are actually reporting the correct precision, on decimal's terms.

In addition, math-based solutions (like multiplying by powers of 10) will likely be very slow (decimal is ~40x slower than double for arithmetic, and you don't want to mix in floating-point either because that's likely to introduce imprecision). Similarly, casting to int or long as a means of truncating is error-prone (decimal has a much greater range than either of those - it's based around a 96-bit integer).

While not elegant as such, the following will likely be one of the fastest way to get the precision (when defined as "decimal places excluding trailing zeroes"):

public static int PrecisionOf(decimal d) {
  var text = d.ToString(System.Globalization.CultureInfo.InvariantCulture).TrimEnd('0');
  var decpoint = text.IndexOf('.');
  if (decpoint < 0)
    return 0;
  return text.Length - decpoint - 1;
}

The invariant culture guarantees a '.' as decimal point, trailing zeroes are trimmed, and then it's just a matter of seeing of how many positions remain after the decimal point (if there even is one).

Edit: changed return type to int

User · Answer

One of the best solutions for finding the number of digits after the decimal point is shown in burning LEGION s post    Here I am using parts from a STSdb forum article  Number of digits after decimal point   In MSDN we can read the following explanation    A decimal number is a floating-point value that consists of a sign  a numeric value where each digit in the value ranges from 0 to 9   and a scaling factor that indicates the position of a floating decimal point that separates the integral and fractional parts of the numeric value    And also    The binary representation of a Decimal value consists of a 1-bit sign  a 96-bit integer number  and a scaling factor used to divide the 96-bit integer  and specify what portion of it is a decimal fraction  The scaling factor is implicitly the number 10  raised to an exponent ranging from 0 to 28    On internal level the decimal value is represented by four integer values     There is a publicly available GetBits function for getting the internal representation  The function returns an int   array      DynamicallyInvokable   public static int   GetBits decimal d        return new int     d lo  d mid  d hi  d flags        The fourth element of the returned array contains a scale factor and a sign  And as the MSDN says the scaling factor is implicitly the number 10  raised to an exponent ranging from 0 to 28  This is exactly what we need   Thus  based on all above investigations we can construct our method   private const int SIGN MASK    Int32 MinValue   public static int GetDigits4 decimal value        return  Decimal GetBits value  3   amp  SIGN MASK   gt  gt  16      Here a SIGN MASK is used to ignore the sign  After logical and we have also shifted the result with 16 bits to the right to receive the actual scale factor  This value  finally  indicates the number of digits after the decimal point   Note that here MSDN also says the scaling factor also preserves any trailing zeros in a Decimal number  Trailing zeros do not affect the value of a Decimal number in arithmetic or comparison operations  However  trailing zeros might be revealed by the ToString method if an appropriate format string is applied    This solutions looks like the best one  but wait  there is more  By accessing private methods in C  we can use expressions to build a direct access to the flags field and avoid constructing the int array   public delegate int GetDigitsDelegate ref Decimal value    public class DecimalHelper       public static readonly DecimalHelper Instance   new DecimalHelper         public readonly GetDigitsDelegate GetDigits      public readonly Expression lt GetDigitsDelegate gt  GetDigitsLambda       public DecimalHelper                 GetDigitsLambda   CreateGetDigitsMethod            GetDigits   GetDigitsLambda Compile               private Expression lt GetDigitsDelegate gt  CreateGetDigitsMethod                 var value   Expression Parameter typeof Decimal  MakeByRefType     value             var digits   Expression RightShift              Expression And Expression Field value   flags    Expression Constant  Int32 MinValue  typeof int                  Expression Constant 16  typeof int                return  value flags  amp   Int32 MinValue   gt  gt  16          return Expression Lambda lt GetDigitsDelegate gt  digits  value             This compiled code is assigned to the GetDigits field  Note that the function receives the decimal value as ref  so no actual copying is performed - only a reference to the value  Using the GetDigits function from the DecimalHelper is easy   decimal value   3 14159m  int digits   DecimalHelper Instance GetDigits ref value     This is the fastest possible method for getting number of digits after decimal point for decimal values

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As a decimal extension method that takes into account   Different cultures Whole numbers Negative numbers Trailing set zeros on the decimal place  e g  1 2300M will return 2 not 4   public static class DecimalExtensions       public static int GetNumberDecimalPlaces this decimal source                var parts   source ToString CultureInfo InvariantCulture  Split                if  parts Length  lt  2              return 0           return parts 1  TrimEnd  0   Length

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I wrote a concise little method yesterday that also returns the number of decimal places without having to rely on any string splits or cultures which is ideal   public int GetDecimalPlaces decimal decimalNumber        try          PRESERVE BEGIN         int decimalPlaces   1          decimal powers   10 0m          if  decimalNumber  gt  0 0m                while   decimalNumber   powers    1    0 0m                    powers    10 0m                    decimalPlaces                          return decimalPlaces

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Relying on the internal representation of decimals is not cool   How about this       int CountDecimalDigits decimal n                return n ToString System Globalization CultureInfo InvariantCulture                     TrimEnd  0   uncomment if you don t want to count trailing zeroes                  SkipWhile c   gt  c                          Skip 1                   Count

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You can try   int priceDecimalPlaces           price ToString System Globalization CultureInfo InvariantCulture                 Split      1  Length

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Since none of the answers supplied were good enough for the magic number  -0 01f  converted to decimal   i e  GetDecimal  decimal -0 01f    I can only assume a colossal mind-fart virus attacked everyone 3 years ago     Here is what seems to be a working implementation to this evil and monstrous problem  the very complicated problem of counting the decimal places after the point - no strings  no cultures  no need to count the bits and no need to read math forums   just simple 3rd grade math   public static class MathDecimals       public static int GetDecimalPlaces decimal n                n   Math Abs n     make sure it is positive          n -   int n        remove the integer part of the number          var decimalPlaces   0          while  n  gt  0                        decimalPlaces                n    10              n -   int n                    return decimalPlaces              private static void Main string   args        Console WriteLine 1 3m     this is 0 3333333333333333333333333333     Console WriteLine 1 3f     this is 0 3333333      Console WriteLine MathDecimals GetDecimalPlaces 0 0m                       0     Console WriteLine MathDecimals GetDecimalPlaces 1 3m                       28     Console WriteLine MathDecimals GetDecimalPlaces  decimal  1   3f           7     Console WriteLine MathDecimals GetDecimalPlaces -1 123m                    3     Console WriteLine MathDecimals GetDecimalPlaces 43 12345m                  5     Console WriteLine MathDecimals GetDecimalPlaces 0                          0     Console WriteLine MathDecimals GetDecimalPlaces 0 01m                      2     Console WriteLine MathDecimals GetDecimalPlaces -0 001m                    3     Console WriteLine MathDecimals GetDecimalPlaces  decimal -0 00000001f      8     Console WriteLine MathDecimals GetDecimalPlaces  decimal 0 0001234f        7     Console WriteLine MathDecimals GetDecimalPlaces  decimal 0 01f             2     Console WriteLine MathDecimals GetDecimalPlaces  decimal -0 01f            2

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I suggest using this method          public static int GetNumberOfDecimalPlaces decimal value  int maxNumber                if  maxNumber    0              return 0           if  maxNumber  gt  28              maxNumber   28           bool isEqual   false          int placeCount   maxNumber          while  placeCount  gt  0                        decimal vl   Math Round value  placeCount - 1               decimal vh   Math Round value  placeCount               isEqual    vl    vh                if  isEqual    false                  break               placeCount--                    return Math Min placeCount  maxNumber

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you can use the InvariantCulture  string priceSameInAllCultures   price ToString System Globalization CultureInfo InvariantCulture     another possibility would be to do something like that   private int GetDecimals decimal d  int i   0        decimal multiplied    decimal   double d   Math Pow 10  i        if  Math Round multiplied     multiplied          return i      return GetDecimals d  i 1

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So far  nearly all of the listed solutions are allocating GC Memory  which is very much the C  way to do things but far from ideal in performance critical environments   The ones that do not allocate use loops and also don t take trailing zeros into consideration    So to avoid GC Allocs  you can just access the scale bits in an unsafe context  That might sound fragile but as per Microsoft s reference source  the struct layout of decimal is Sequential and even has a comment in there  not to change the order of the fields          NOTE  Do not change the order in which these fields are declared  The        native methods in this class rely on this particular order      private int flags      private int hi      private int lo      private int mid    As you can see  the first int here is the flags field  From the documentation and as mentioned in other comments here  we know that only the bits from 16-24 encode the scale and that we need to avoid the 31st bit which encodes the sign  Since int is the size of 4 bytes  we can safely do this   internal static class DecimalExtensions     public static byte GetScale this decimal value          unsafe             byte  v    byte   amp value        return v 2                 This should be the most performant solution since there is no GC alloc of the bytes array or ToString conversions  I ve tested it against  Net 4 x and  Net 3 5 in Unity 2019 1  If there are any versions where this does fail  please let me know   Edit   Thanks to  Zastai for reminding me about the possibility to use an explicit struct layout to practically achieve the same pointer logic outside of unsafe code    StructLayout LayoutKind Explicit   public struct DecimalHelper       const byte k SignBit   1  lt  lt  7        FieldOffset 0       public decimal Value        FieldOffset 0       public readonly uint Flags       FieldOffset 0       public readonly ushort Reserved       FieldOffset 2       byte m Scale      public byte Scale               get                       return m Scale                    set                       if value  gt  28                  throw new System ArgumentOutOfRangeException  value    Scale can t be bigger than 28                m Scale   value                       FieldOffset 3       byte m SignByte      public int Sign               get                       return m SignByte  gt  0   -1   1                      public bool Positive               get                       return  m SignByte  amp  k SignBit   gt  0                     set                       m SignByte   value    byte 0   k SignBit                       FieldOffset 4       public uint Hi       FieldOffset 8       public uint Lo       FieldOffset 12       public uint Mid       public DecimalHelper decimal value    this                 Value   value             public static implicit operator DecimalHelper decimal value                return new DecimalHelper value              public static implicit operator decimal DecimalHelper value                return value Value            To solve the original problem  you could strip away all fields besides Value and Scale but maybe it could be useful for someone to have them all

User · Answer

I used Joe s way to solve this issue     decimal argument   123 456m  int count   BitConverter GetBytes decimal GetBits argument  3   2

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And here s another way  use the type SqlDecimal which has a scale property with the count of the digits right of the decimal   Cast your decimal value to SqlDecimal and then access Scale     SqlDecimal  decimal yourValue  Scale

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string number    123 456789      Convert to string int length   number Substring number IndexOf        1  Length      6

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I m using something very similar to Clement s answer   private int GetSignificantDecimalPlaces decimal number  bool trimTrailingZeros   true      string stemp   Convert ToString number      if  trimTrailingZeros      stemp   stemp TrimEnd  0       return stemp Length - 1 - stemp IndexOf           Application CurrentCulture NumberFormat NumberDecimalSeparator       Remember to use System Windows Forms to get access to Application CurrentCulture

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I use the following mechanism in my code    public static int GetDecimalLength string tempValue                int decimalLength   0          if  tempValue Contains         tempValue Contains                             char   separator   new char                             string   tempstring   tempValue Split separator                decimalLength   tempstring 1  Length                    return decimalLength          decimal input 3 376  var instring input ToString     call GetDecimalLength instring

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Using recursion you can do     private int GetDecimals decimal n  int decimals   0            return n   1    0   GetDecimals n   10  decimals   1    decimals

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I d probably use the solution in  fixagon s answer   However  while the Decimal struct doesn t have a method to get the number of decimals  you could call Decimal GetBits to extract the binary representation  then use the integer value and scale to compute the number of decimals   This would probably be faster than formatting as a string  though you d have to be processing an awful lot of decimals to notice the difference   I ll leave the implementation as an exercise

[c#] Find number of decimal places in decimal value regardless of culture

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