[C#]String Formatting 정리

String Formatting C# String Format for Double ? format float numbers C# String Format for Int ? format (align) integer numbers C# String Format for DateTime ? format date and time C# Align String with Spaces ? how to align text to the right or left C# Indent String with Spaces ? how to indent text with repeated spaces C# IFormatProvider for Numbers ? parse float numbers with IFormatProvider C# Custom IFormatProvider ? string formatting with custom IFormatProvider String Format for Double [C#] The following examples show how to format float numbers to string in C#. You can use static method String.Format or instance methods double.ToString and float.ToString. Digits after decimal point This example formats double to string with fixed number of decimal places. For two decimal places use pattern ?0.00“. If a float number has less decimal places, the rest digits on the right will be zeroes. If it has more decimal places, the number will be rounded. [C#] // just two decimal places String.Format("{0:0.00}", 123.4567);      // "123.46" String.Format("{0:0.00}", 123.4);         // "123.40" String.Format("{0:0.00}", 123.0);         // "123.00"   Next example formats double to string with floating number of decimal places. E.g. for maximal two decimal places use pattern ?0.##“. [C#] // max. two decimal places String.Format("{0:0.##}", 123.4567);      // "123.46" String.Format("{0:0.##}", 123.4);         // "123.4" String.Format("{0:0.##}", 123.0);         // "123"   Digits before decimal point If you want a float number to have any minimal number of digits before decimal point use N-times zero before decimal point. E.g. pattern ?00.0“ formats a float number to string with at least two digits before decimal point and one digit after that. [C#] // at least two digits before decimal point String.Format("{0:00.0}", 123.4567);      // "123.5" String.Format("{0:00.0}", 23.4567);       // "23.5" String.Format("{0:00.0}", 3.4567);        // "03.5" String.Format("{0:00.0}", -3.4567);       // "-03.5"   Thousands separator To format double to string with use of thousands separator use zero and comma separator before an usual float formatting pattern, e.g. pattern ?0,0.0“ formats the number to use thousands separators and to have one decimal place. [C#] String.Format("{0:0,0.0}", 12345.67);     // "12,345.7" String.Format("{0:0,0}", 12345.67);       // "12,346"   Zero Float numbers between zero and one can be formatted in two ways, with or without leading zero before decimal point. To format number without a leading zero use # before point. For example ?#.0“ formats number to have one decimal place and zero to N digits before decimal point (e.g. ?.5“ or ?123.5“). Following code shows how can be formatted a zero (of double type). [C#] String.Format("{0:0.0}", 0.0);            // "0.0" String.Format("{0:0.#}", 0.0);            // "0" String.Format("{0:#.0}", 0.0);            // ".0" String.Format("{0:#.#}", 0.0);            // ""   Align numbers with spaces To align float number to the right use comma ?,“ option before the colon. Type comma followed by a number of spaces, e.g. ?0,10:0.0“ (this can be used only in String.Format method, not in double.ToString method). To align numbers to the left use negative number of spaces. [C#] String.Format("{0,10:0.0}", 123.4567);    // "     123.5" String.Format("{0,-10:0.0}", 123.4567);   // "123.5     " String.Format("{0,10:0.0}", -123.4567);   // "    -123.5" String.Format("{0,-10:0.0}", -123.4567);  // "-123.5    "   Custom formatting for negative numbers and zero If you need to use custom format for negative float numbers or zero, use semicolon separator ?;“ to split pattern to three sections. The first section formats positive numbers, the second section formats negative numbers and the third section formats zero. If you omit the last section, zero will be formatted using the first section. [C#] String.Format("{0:0.00;minus 0.00;zero}", 123.4567);   // "123.46" String.Format("{0:0.00;minus 0.00;zero}", -123.4567);  // "minus 123.46" String.Format("{0:0.00;minus 0.00;zero}", 0.0);        // "zero"   Some funny examples As you could notice in the previous example, you can put any text into formatting pattern, e.g. before an usual pattern ?my text 0.0“. You can even put any text between the zeroes, e.g. ?0aaa.bbb0“. [C#] String.Format("{0:my number is 0.0}", 12.3);   // "my number is 12.3" String.Format("{0:0aaa.bbb0}", 12.3);          // "12aaa.bbb3"   String Format for Int [C#] Integer numbers can be formatted in .NET in many ways. You can use static method String.Format or instance method int.ToString. Following examples shows how to align numbers (with spaces or zeroes), how to format negative numbers or how to do custom formatting like phone numbers. Add zeroes before number To add zeroes before a number, use colon separator ?:“ and write as many zeroes as you want. [C#] String.Format("{0:00000}", 15);          // "00015" String.Format("{0:00000}", -15);         // "-00015"   Align number to the right or left To align number to the right, use comma ?,“ followed by a number of characters. This alignment option must be before the colon separator. [C#] String.Format("{0,5}", 15);              // "   15" String.Format("{0,-5}", 15);             // "15   " String.Format("{0,5:000}", 15);          // "  015" String.Format("{0,-5:000}", 15);         // "015  "   Different formatting for negative numbers and zero You can have special format for negative numbers and zero. Use semicolon separator ?;“ to separate formatting to two or three sections. The second section is format for negative numbers, the third section is for zero. [C#] String.Format("{0:#;minus #}", 15);      // "15" String.Format("{0:#;minus #}", -15);     // "minus 15" String.Format("{0:#;minus #;zero}", 0);  // "zero"   Custom number formatting (e.g. phone number) Numbers can be formatted also to any custom format, e.g. like phone numbers or serial numbers. [C#] String.Format("{0:+### ### ### ###}", 447900123456); // "+447 900 123 456" String.Format("{0:##-####-####}", 8958712551);       // "89-5871-2551"   String Format for DateTime [C#] This example shows how to format DateTime using String.Format method. All formatting can be done also using DateTime.ToString method. Custom DateTime Formatting There are following custom format specifiers y (year), M (month), d (day), h (hour 12), H (hour 24), m (minute), s (second), f (second fraction), F (second fraction, trailing zeroes are trimmed), t (P.M or A.M) and z (time zone). Following examples demonstrate how are the format specifiers rewritten to the output. [C#] // create date time 2008-03-09 16:05:07.123 DateTime dt = new DateTime(2008, 3, 9, 16, 5, 7, 123);   String.Format("{0:y yy yyy yyyy}", dt);  // "8 08 008 2008"   year String.Format("{0:M MM MMM MMMM}", dt);  // "3 03 Mar March"  month String.Format("{0:d dd ddd dddd}", dt);  // "9 09 Sun Sunday" day String.Format("{0:h hh H HH}",     dt);  // "4 04 16 16"      hour 12/24 String.Format("{0:m mm}",          dt);  // "5 05"            minute String.Format("{0:s ss}",          dt);  // "7 07"            second String.Format("{0:f ff fff ffff}", dt);  // "1 12 123 1230"   sec.fraction String.Format("{0:F FF FFF FFFF}", dt);  // "1 12 123 123"    without zeroes String.Format("{0:t tt}",          dt);  // "P PM"            A.M. or P.M. String.Format("{0:z zz zzz}",      dt);  // "-6 -06 -06:00"   time zone   You can use also date separator / (slash) and time sepatator : (colon). These characters will be rewritten to characters defined in the current DateTimeForma­tInfo.DateSepa­rator and DateTimeForma­tInfo.TimeSepa­rator. [C#] // date separator in german culture is "." (so "/" changes to ".") String.Format("{0:d/M/yyyy HH:mm:ss}", dt); // "9/3/2008 16:05:07" - english (en-US) String.Format("{0:d/M/yyyy HH:mm:ss}", dt); // "9.3.2008 16:05:07" - german (de-DE)   Here are some examples of custom date and time formatting: [C#] // month/day numbers without/with leading zeroes String.Format("{0:M/d/yyyy}", dt);            // "3/9/2008" String.Format("{0:MM/dd/yyyy}", dt);          // "03/09/2008"   // day/month names String.Format("{0:ddd, MMM d, yyyy}", dt);    // "Sun, Mar 9, 2008" String.Format("{0:dddd, MMMM d, yyyy}", dt);  // "Sunday, March 9, 2008"   // two/four digit year String.Format("{0:MM/dd/yy}", dt);            // "03/09/08" String.Format("{0:MM/dd/yyyy}", dt);          // "03/09/2008"   Standard DateTime Formatting In DateTimeForma­tInfo there are defined standard patterns for the current culture. For example property ShortTimePattern is string that contains value h:mm tt for en-US culture and value HH:mm for de-DE culture. Following table shows patterns defined in DateTimeForma­tInfo and their values for en-US culture. First column contains format specifiers for the String.Format method. Specifier DateTimeFormatInfo property Pattern value (for en-US culture) t ShortTimePattern h:mm tt d ShortDatePattern M/d/yyyy T LongTimePattern h:mm:ss tt D LongDatePattern dddd, MMMM dd, yyyy f (combination of D and t) dddd, MMMM dd, yyyy h:mm tt F FullDateTimePattern dddd, MMMM dd, yyyy h:mm:ss tt g (combination of d and t) M/d/yyyy h:mm tt G (combination of d and T) M/d/yyyy h:mm:ss tt m, M MonthDayPattern MMMM dd y, Y YearMonthPattern MMMM, yyyy r, R RFC1123Pattern ddd, dd MMM yyyy HH':'mm':'ss 'GMT' (*) s SortableDateTi­mePattern yyyy'-'MM'-'dd'T'HH':'mm':'ss (*) u UniversalSorta­bleDateTimePat­tern yyyy'-'MM'-'dd HH':'mm':'ss'Z' (*)     (*) = culture independent Following examples show usage of standard format specifiers in String.Format method and the resulting output. [C#] String.Format("{0:t}", dt);  // "4:05 PM"                         ShortTime String.Format("{0:d}", dt);  // "3/9/2008"                        ShortDate String.Format("{0:T}", dt);  // "4:05:07 PM"                      LongTime String.Format("{0:D}", dt);  // "Sunday, March 09, 2008"          LongDate String.Format("{0:f}", dt);  // "Sunday, March 09, 2008 4:05 PM"  LongDate+ShortTime String.Format("{0:F}", dt);  // "Sunday, March 09, 2008 4:05:07 PM" FullDateTime String.Format("{0:g}", dt);  // "3/9/2008 4:05 PM"                ShortDate+ShortTime String.Format("{0:G}", dt);  // "3/9/2008 4:05:07 PM"             ShortDate+LongTime String.Format("{0:m}", dt);  // "March 09"                        MonthDay String.Format("{0:y}", dt);  // "March, 2008"                     YearMonth String.Format("{0:r}", dt);  // "Sun, 09 Mar 2008 16:05:07 GMT"   RFC1123 String.Format("{0:s}", dt);  // "2008-03-09T16:05:07"             SortableDateTime String.Format("{0:u}", dt);  // "2008-03-09 16:05:07Z"            UniversalSortableDateTime   Align String with Spaces [C#] This example shows how to align strings with spaces. The example formats text to table and writes it to console output. To align string to the right or to the left use static method String.Format. To align string to the left (spaces on the right) use formatting patern with comma (,) followed by a negative number of characters: String.Format(?{0,?10}“, text). To right alignment use a positive number: {0,10}. Following example shows how to format text to the table. Values in the first and second column are aligned to the left and the third column is aligned to the right. [C#] Console.WriteLine("-------------------------------"); Console.WriteLine("First Name | Last Name  |   Age"); Console.WriteLine("-------------------------------"); Console.WriteLine(String.Format("{0,-10} | {1,-10} | {2,5}", "Bill", "Gates", 51)); Console.WriteLine(String.Format("{0,-10} | {1,-10} | {2,5}", "Edna", "Parker", 114)); Console.WriteLine(String.Format("{0,-10} | {1,-10} | {2,5}", "Johnny", "Depp", 44)); Console.WriteLine("-------------------------------");   Output string:  ------------------------------- First Name | Last Name  |   Age ------------------------------- Bill       | Gates      |    51 Edna       | Parker     |   114 Johnny     | Depp       |    44 ------------------------------- Indent String with Spaces [C#] This example shows how to indent strings using method for padding in C#. To repeat spaces use method String.PadLeft. If you call ?hello“.PadLeft(10) you will get the string aligned to the right: ?     hello“. If you use empty string instead of the ?hello“ string the result will be 10× repeated space character. This can be used to create simple Indent method. The Indent method: [C#] public static string Indent(int count) {     return "".PadLeft(count); }   Test code: [C#] Console.WriteLine(Indent(0) + "List"); Console.WriteLine(Indent(3) + "Item 1"); Console.WriteLine(Indent(6) + "Item 1.1"); Console.WriteLine(Indent(6) + "Item 1.2"); Console.WriteLine(Indent(3) + "Item 2"); Console.WriteLine(Indent(6) + "Item 2.1");   Output string: List    Item 1       Item 1.1       Item 1.2    Item 2       Item 2.1 IFormatProvider for Numbers [C#] This example shows how to convert float to string and string to float using IFormatProvider. To get IFormatProvider you need to get CultureInfo instance first. Get invariant or specific CultureInfo Invariant culture is a special type of culture which is culture-insensitive. You should use this culture when you need culture-independent results, e.g. when you format or parse values in XML file. The invariant culture is internally associated with the English language. To get invariant CultureInfo instance use static property CultureInfo.In­variantCulture. To get specific CultureInfo instance use static method CultureInfo.Get­CultureInfo with the specific culture name, e.g. for the German language CultureInfo.GetCultureInfo("de-DE"). Format and parse numbers using the IFormatProvider Once you have the CultureInfo instance use property CultureInfo.Num­berFormat to get an IFormatProvider for numbers (the NumberFormatInfo object) [C#] // format float to string float num = 1.5f; string str = num.ToString(CultureInfo.InvariantCulture.NumberFormat);        // "1.5" string str = num.ToString(CultureInfo.GetCultureInfo("de-DE").NumberFormat); // "1,5"   [C#] // parse float from string float num = float.Parse("1.5", CultureInfo.InvariantCulture.NumberFormat); float num = float.Parse("1,5", CultureInfo.GetCultureInfo("de-DE").NumberFormat);   Custom IFormatProvider [C#] The following example shows how to write a custom IFormatProvider which you can use in method String.Format(I­FormatProvider, …). This formatter formats doubles to 3 decimal places with a dot separator. [C#] public class DoubleFormatter : IFormatProvider, ICustomFormatter {   // always use dot separator for doubles   private CultureInfo enUsCulture = CultureInfo.GetCultureInfo("en-US");     public string Format(string format, object arg, IFormatProvider formatProvider)   {     // format doubles to 3 decimal places     return string.Format(enUsCulture, "{0:0.000}", arg);   }     public object GetFormat(Type formatType)   {     return (formatType == typeof(ICustomFormatter)) ? this : null;   } }   Having this formatter, we can use it like this: [C#] double width = 15.77555; double height = 12.8497979; Console.WriteLine(   string.Format(new DoubleFormatter(), "w={0} h={1}", width, height));   Output: w=15.776 h=12.850 So now we have a reusable format for doubles ? 3 decimal places with dot separator. That is nice, but this formatter is very simple ? it formats everything (eg. DateTime) as ?0:000“. This is a fast version if you know that you will only use it for formatting lots of doubles. The real version should look like this: [C#] public class DoubleFormatter : IFormatProvider, ICustomFormatter {   // always use dot separator for doubles   private CultureInfo enUsCulture = CultureInfo.GetCultureInfo("en-US");     public string Format(string format, object arg, IFormatProvider formatProvider)   {     if (arg is double)     {       if (string.IsNullOrEmpty(format))       {         // by default, format doubles to 3 decimal places         return string.Format(enUsCulture, "{0:0.000}", arg);       }       else       {         // if user supplied own format use it         return ((double)arg).ToString(format, enUsCulture);       }     }     // format everything else normally     if (arg is IFormattable)       return ((IFormattable)arg).ToString(format, formatProvider);     else       return arg.ToString();  }     public object GetFormat(Type formatType)   {     return (formatType == typeof(ICustomFormatter)) ? this : null;   } }   Example: [C#] Console.WriteLine(string.Format(new DoubleFormatter(), "Numbers {0} and {1:0.0}. Now a string {2}, a number {3}, date {4} and object: {5}", 1.234567, -0.57123456, "Hi!", 5, DateTime.Now, new object()));   Output: Numbers 1.235 and -0.6. Now a string Hi!, a number 5, date 12.6.2009 17:11:35 and object: System.Object Other examples with custom formatters can be found in MSDN. See example with formatter for 12-digit account numbers (12345?678?9012) or example with binary, octal, and hexadecimal formatter.