C# format strings

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Details

Last Updated on 13 September 2011

Written by Jaap de Haan

Hits: 7082

Syntax

Formatting is bound to a type, so depending on which type of object you pass to String.Format, you have different format specifiers.

The index specifies the position of the parameter that shall be used for that format specifier. It can be repeated!

When implementing custom formating, try to stick to this behaviour for being consistent with the default implementation.

• Generic, alignment is applied after type formatting, so can be used for all types
  • {index[,alignment][:format]}
• For numerical values (; separator):
  • {index[,alignment]:format >= 0;format < 0}
  • {index[,alignment]:format > 0;format < 0;format = 0}

Pitfalls and gotchas

Pitfalls for specific types are illustrated at the bottom of the type specific parts. Generally speaking, the biggest gotcha is that you should use the invariant culture if you want to have culture independent output. This matters a lot for serialization, because ToString() might yield different results depending on the culture of the current thread.

String

Alignment is the only formatting you can apply to a string but it works for all types. [Object := Text (String)]

{0,-10}

Text......

Text......

{0,10}

......Text

......Text

{0}

Text

Text

if (...) {

System.FormatException

System.FormatException

if (...) {{

if (...) {

if (...) {

Generic numeric values (conventions)

• 0    zero placeholder
• #    digit placeholder
• .    decimal point
• ,    thousand separator
• %    multiplies by 100, adds % sign
• ‰    multiplies by 100, adds ‰ sign ('\u2030')
• e    exponent placeholder

Integer types

Iinteger patterns [Object := 1234 (Int32)]

{0}

1234

1234

{0:0,000.0}

1,234.0

1.234,0

{0:(#) #-##}

(1) 2-34

(1) 2-34

{0:D}

1234

1234

{0:D6}

001234

001234

{0:x}

4d2

4d2

{0:x4}

04d2

04d2

{0:X}

4D2

4D2

{0:X5}

004D2

004D2

{0:#.##}

1234

1234

{0:0.00}

1234.00

1234,00

{0:#-##-##}

-12-34

-12-34

{0:0,0}

1,234

1.234

Floating point types

Double, Float used for scientific notation or currency output.

TO BE DONE (visit us again later, ...)

Enumerated types

g, G    display the enum as text if Flags attribute or single value
f, F    display the enum as text (finds a matching sum), if fails falls back to integer
d, D    decimal value display (no leading zeroes)
x, X    hexadecimal value display with at least 8 digits

TO BE DONE: examples of output with Flags, ... (give us a visit later again, ...)

Date/Time - Generic Patterns

DateTime patterns [Object := 2009-10-24T13:47:32.0534529 (DateTime)]

{0}

{0:d}

{0:D}

{0:t}

{0:T}

{0:f}

{0:F}

{0:g}

{0:G}

{0:M}

{0:y}

{0:r}

{0:o}

{0:s}

{0:u}

{0:U}

Date/Time - Custom Patterns

DateTime custom patterns [Object := 2009-10-24T13:47:32.0534529 (DateTime)]

{0:dd}

{0:ddd}

{0:dddd}

{0:MM}

{0:MMM}

{0:MMMM}

{0:yy}

{0:yyyy}

{0:gg}

{0:hh}

{0:HH}

{0:tt}

{0:zz}

{0:zzz}

{0:mm}

{0:ss}

{0:ff}

{0:fff}

{0:ffffff}

{0:dd/mm/yyyy}

{0:dd/MM/yyyy}

{0:dd/MM/yyyy}

{0:dd'/'MM'/'yyyy}

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