A cheat sheet with everything there is to know about formatting the primitive types, DateTimes and TimeSpans in .NET.

Stringify

The different ways of formatting these ValueTypes.

// ValueType.ToString("format");
Console.Write(5000.ToString("#,##0"));

// Composite Formatting
Console.WriteLine("{0:yyyy-MM-dd HH:mm:ss}", DateTime.Now);

var str = new StringBuilder();
str.AppendFormat("{0:F} - {1:0.00}", 1, 2);

using (var stream = new StreamWriter(@"c:\temp\aargh.txt"))
{
	stream.Write("{0} -> {1}", 1, 2);
}

// String interpolation
int i = 5;
Debug.WriteLine($"{i:F}");

// Escaping {}
Debug.WriteLine("{{0}} = {0}", 5); // {0} = 5
// Nested braces like {{0:D}} are NOT supported

// Optional alignment component
// Positive: Right-align
// Negative: Left-align
var table = new StringBuilder();
table.AppendFormat("{0,-10} | {1,5}\n", "Name", "Age");
table.AppendFormat("{0,-10} | {1,5:F}\n", "Bob", 18);
table.AppendFormat("{0,-10} | {1,5:F}\n", "Alice", 24);
table.AppendFormat("{0,-10} | {1,5:F}\n", "Methuselah", 969);

// table.ToString():
Name       |   Age
Bob        | 18.00
Alice      | 24.00
Methuselah | 969.00

Cultures

The culture for all threads defaults to the Windows system culture.

using System.Threading;
using System.Globalization;

// Number, Date, ... formatting
Thread.CurrentThread.CurrentCulture = new CultureInfo("en-US");

// Translations from ResX files
Thread.CurrentThread.CurrentUICulture = new CultureInfo("en-US");

Starting from .NET Framework 4.5, default cultures can be set for all new and all existing threads in the AppDomain that have not explicitely set their CurrentThread.CurrentCulture.

CultureInfo.DefaultThreadCurrentCulture = new CultureInfo("en-US");
CultureInfo.DefaultThreadCurrentUICulture = new CultureInfo("en-US");

Number Formatting

Standard Numeric Formats

decimal m = 1000.5050M;
string pretty = money.ToString(SomeFormat);

SomeFormat is case insensitive. All standard numeric formats may be suffixed with an optional precision specifier. If no number is provided, it defaults to the value of CurrencyDecimalDigits in the configuration of the current culture NumberFormatInfo.

Thread.CurrentThread.CurrentCulture.NumberFormat

Other standard numeric formats:

// Pad integral types (int, byte, long, ...)
15.ToString("D4"); // 0015

// Fixed point
15.495.ToString("F"); // 15.50

// Round-trip (Single, Double, BigInteger)
// ATTN: /platform:x64 vs /platform:anycpu (Use "G17" instead?)
(15.0123453f).ToString("N7"); // 15.0123500
(15.0123453f).ToString("R0"); // 15.0123453

// "E" => Exponential notation
// "G" => General, the more compact of either "F" or "E" (default)
// "X" => Hexidecimal (integral only)

Custom formats:

// Explicitly show the +/- sign
10.ToString("positive;negative;zero"); // positive
10.ToString("+#;-#;0"); // +10
0.ToString("+0;-0"); // +0

// Percentage (NumberFormatInfo.PercentSymbol)
0.01.ToString("#%"); // 1%

// ‰ == "\u2030" (Per mille)
0.01.ToString("#\u2030"); // 10‰

// , is also used as number scaling specifier
// Where each , divides the number by 1000
123456789.ToString("#,,"); // 123

// Bananas (https://www.youtube.com/watch?v=EdR72ACz_xI)
1234586789.ToString(@"\##,##0.00\#"); // #1,234,586,789.00#
1234586789.ToString(@"\##,##0,,.00\#"); // #1,234.59#
8009999999.ToString("000-000-0000"); // 800-999-9999

Date Formatting

Standard Date and Time Format Strings

Configuration: System.Globalization.DateTimeFormatInfo

var dt = new DateTime(2017, 1, 31, 22, 15, 59);

Culture insensitive formats

var dt = new DateTime(2017, 1, 31, 22, 15, 59);
var dto = new DateTimeOffset(dt, TimeSpan.FromHours(2));

Custom Date and Time Format Strings

// Use % for single character custom formats
DateTime.Now.ToString("%M");

// Other:
// g -> A.D
// K -> Time zone info: Kind Unspecified, Kind Utc, Kind Local or -01:00
// fff -> Milliseconds (Other from f to FFFFFFF)
// z -> Hours offset from Utc

TimeSpan Formatting

var span = new TimeSpan(31, 22, 15, 59);

The square brackets will omit the part if not significant. They are not valid as custom format.

Custom formats:
Like Date Custom formats but each part represents the whole part in the time interval.

span.ToString(@"dd\.hh\:mm\:ss"); // 31.22:15:59
Console.WriteLine("{0:%d}", span); // 31
Console.WriteLine("{0:ddddd}", span); // 00031