Wednesday, November 5, 2008

Csharp String.Format

Strings

There really isn�t any formatting within a string, beyond it�s alignment. Alignment works for any argument being printed in a String.Format call.

SampleGenerates
String.Format("->{1,10}<-", "Hello");-> Hello<-
String.Format("->{1,-10}<-", "Hello");->Hello <-

Numbers

Basic number formatting specifiers:

SpecifierTypeFormat Output (Passed Double 1.42)Output (Passed Int -12400)
cCurrency{0:c}$1.42-$12,400
dDecimal (Whole number){0:d}System.FormatException-12400
eScientific{0:e}1.420000e+000-1.240000e+004
fFixed point{0:f}1.42-12400.00
gGeneral{0:g}1.42-12400
nNumber with commas for thousands{0:n}1.42-12,400
rRound trippable{0:r}1.42System.FormatException
xHexadecimal{0:x4}System.FormatExceptioncf90

Custom number formatting:

SpecifierTypeExample Output (Passed Double 1500.42)Note
0Zero placeholder{0:00.0000}1500.4200Pads with zeroes.
#Digit placeholder{0:(#).##}(1500).42
.Decimal point{0:0.0}1500.4
,Thousand separator{0:0,0}1,500Must be between two zeroes.
,.Number scaling{0:0,.} 2Comma adjacent to Period scales by 1000.
%Percent{0:0%}150042%Multiplies by 100, adds % sign.
eExponent placeholder{0:00e+0}15e+2Many exponent formats available.
;Group separatorsee below

The group separator is especially useful for formatting currency values which require that negative values be enclosed in parentheses. This currency formatting example at the bottom of this document makes it obvious:

Dates

Note that date formatting is especially dependant on the system�s regional settings; the example strings here are from my local locale.

SpecifierTypeExample (Passed System.DateTime.Now)
dShort date10/12/2002
DLong dateDecember 10, 2002
tShort time10:11 PM
TLong time10:11:29 PM
fFull date & time December 10, 2002 10:11 PM
FFull date & time (long)December 10, 2002 10:11:29 PM
gDefault date & time10/12/2002 10:11 PM
GDefault date & time (long)10/12/2002 10:11:29 PM
MMonth day patternDecember 10
rRFC1123 date stringTue, 10 Dec 2002 22:11:29 GMT
sSortable date string2002-12-10T22:11:29
uUniversal sortable, local time2002-12-10 22:13:50Z
UUniversal sortable, GMTDecember 11, 2002 3:13:50 AM
YYear month patternDecember, 2002

The �U� specifier seems broken; that string certainly isn�t sortable.

Custom date formatting:

SpecifierTypeExample Example Output
ddDay{0:dd}10
dddDay name{0:ddd}Tue
ddddFull day name{0:dddd}Tuesday
f, ff, �Second fractions{0:fff}932
gg, �Era{0:gg}A.D.
hh2 digit hour{0:hh}10
HH2 digit hour, 24hr format{0:HH}22
mmMinute 00-59{0:mm}38
MMMonth 01-12{0:MM}12
MMMMonth abbreviation{0:MMM}Dec
MMMMFull month name{0:MMMM}December
ssSeconds 00-59{0:ss}46
ttAM or PM{0:tt}PM
yyYear, 2 digits{0:yy}02
yyyyYear{0:yyyy}2002
zzTimezone offset, 2 digits{0:zz}-05
zzzFull timezone offset{0:zzz}-05:00
:Separator{0:hh:mm:ss}10:43:20
/Separator{0:dd/MM/yyyy}10/12/2002

Enumerations

SpecifierType
gDefault (Flag names if available, otherwise decimal)
fFlags always
dInteger always
xEight digit hex.

Some Useful Examples

String.Format("{0:$#,##0.00;($#,##0.00);Zero}",value);

This will output "$1,240.00" if passed 1243.50. It will output the same format but in parentheses if the number is negative, and will output the string "Zero" if the number is zero.

String.Format("{0:(###) ###-####}", 8005551212);

This will output "(800) 555-1212".

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