Chapter12:String.Format

TheFormatmethodsareasetofoverloadsintheSystem.Stringclassusedtocreatestringsthatcombineobjects intospecificstringrepresentations.ThisinformationcanbeappliedtoString.Format,variousWriteLinemethods aswellasothermethodsinthe.NETframework.

Section12.1:SinceC#6.0

Version ≥ 6.0

SinceC#6.0itispossibletousestringinterpolationinplaceofString.Format.

stringname=”John”;

stringlastname=”Doe”;

Console.WriteLine($”Hello{name}{lastname}!”);

Hello JohnDoe!

MoreexamplesforthisunderthetopicC#6.0features:Stringinterpolation.

Section12.2:PlaceswhereString.Formatis’embedded’inthe framework

ThereareseveralplaceswhereyoucanuseString.Formatindirectly:Thesecretistolookfortheoverloadwiththe signaturestringformat,paramsobject[]args,e.g.:

Console.WriteLine(String.Format(“{0}-{1}”,name,value));

Canbe replacedwith shorterversion:

Console.WriteLine(“{0}-{1}”,name,value);

ThereareothermethodswhichalsouseString.Formate.g.:

Debug.WriteLine();//andPrint()

StringBuilder.AppendFormat();

Section12.3:Createacustomformatprovider

publicclassCustomFormat:IFormatProvider,ICustomFormatter

{

publicstringFormat(stringformat,objectarg,IFormatProviderformatProvider)

{

if(!this.Equals(formatProvider))

{

returnnull;

}

if(format==”Reverse”)

{

returnString.Join(“”,arg.ToString().Reverse());

}

returnarg.ToString();

}

publicobjectGetFormat(TypeformatType)

{

returnformatType==typeof(ICustomFormatter)?this:null;

}

}

Usage:

String.Format(newCustomFormat(),”->{0:Reverse}<-“,”HelloWorld”);

Output:

->dlroWolleH<-

Section12.4:DateFormatting

DateTimedate=newDateTime(2016,07,06,18,30,14);

//Format:year,month,dayhours,minutes,seconds

Console.Write(String.Format(“{0:dd}”,date));

//FormatbyCultureinfo

String.Format(newSystem.Globalization.CultureInfo(“mn-MN”),”{0:dddd}”,date);

Version ≥ 6.0

Console.Write($”{date:ddd}”);

06
Лхагва
06
Specifier Meaning Sample Result
d Date {0:d} 7/6/2016
dd Day,zero-padded {0:dd} 06
ddd Shortdayname {0:ddd} Wed
dddd Fulldayname {0:dddd} Wednesday
D Longdate {0:D} Wednesday,July6,2016
f Fulldateandtime,short {0:f} Wednesday,July6,20166:30PM
ff Secondfractions,2digits {0:ff} 20
fff Secondfractions,3digits {0:fff} 201
ffff Secondfractions,4digits {0:ffff} 2016
F Fulldateandtime,long {0:F} Wednesday,July6,20166:30:14PM

g Defaultdateandtime {0:g} 7/6/20166:30 PM
gg Era {0:gg} A.D
hh Hour(2digits,12H) {0:hh} 06
HH Hour(2digits,24H) {0:HH} 18
M Monthandday {0:M} July6
mm Minutes,zero-padded {0:mm} 30
MM Month,zero-padded {0:MM} 07
MMM 3-lettermonthname {0:MMM} Jul
MMMM Fullmonthname {0:MMMM} July
ss Seconds {0:ss} 14
r RFC1123date {0:r} Wed,06Jul201618:30:14GMT
s Sortabledatestring {0:s} 2016-07-06T18:30:14
t Shorttime {0:t} 6:30PM
T Longtime {0:T} 6:30:14PM
tt AM/PM {0:tt} PM
u Universalsortablelocaltime {0:u} 2016-07-0618:30:14Z
U UniversalGMT {0:U} Wednesday,July6,20169:30:14AM
Y Monthandyear {0:Y} July2016
yy 2digityear {0:yy} 16
yyyy 4digityear {0:yyyy} 2016
zz 2digittimezoneoffset {0:zz} +09
zzz fulltimezoneoffset {0:zzz} +09:00

Section12.5:CurrencyFormatting

The”c” (orcurrency) formatspecifier converts anumber toa stringthat represents acurrency amount.

string.Format(“{0:c}”,112.236677)//$112.23-defaultstosystem

Precision

Defaultis2.Usec1,c2,c3andsoontocontrolprecision.

string.Format(“{0:C1}”, 112.236677) //$112.2
string.Format(“{0:C3}”, 112.236677) //$112.237
string.Format(“{0:C4}”, 112.236677) //$112.2367
string.Format(“{0:C9}”, 112.236677) //$112.236677000

CurrencySymbol

1. PassCultureInfoinstancetousecustomculturesymbol.

string.Format(newCultureInfo(“en-US”),”{0:c}”,112.236677);//$112.24

string.Format(newCultureInfo(“de-

DE”),”{0:c}”,112.236677);//112,24€string.Format(newCultureInfo(“hi-

IN”),”{0:c}”,112.236677);//□112.24

2. Useanystringascurrencysymbol.UseNumberFormatInfoastocustomizecurrency symbol.

NumberFormatInfonfi=newCultureInfo(“en-US”,false).NumberFormat;

nfi=(NumberFormatInfo)nfi.Clone();

nfi.CurrencySymbol=”?”;

string.Format(nfi,”{0:C}”,112.236677);//?112.24

nfi.CurrencySymbol=”?%^&”;

string.Format(nfi,”{0:C}”,112.236677);//?%^&112.24

PositionofCurrencySymbol

UseCurrencyPositivePatternforpositivevaluesandCurrencyNegativePatternfornegativevalues.

NumberFormatInfonfi=newCultureInfo(“en-US”,false).NumberFormat; nfi.CurrencyPositivePattern=0;

string.Format(nfi,”{0:C}”,112.236677);//$112.24-default

nfi.CurrencyPositivePattern=1;

string.Format(nfi,”{0:C}”,112.236677);//112.24$

nfi.CurrencyPositivePattern=2;

string.Format(nfi,”{0:C}”,112.236677);//$112.24

nfi.CurrencyPositivePattern=3;string.Format(nfi,”{0:C

}”,112.236677);//112.24$

Negativepatternusageisthesameaspositivepattern.Alotmoreusecasespleaserefertooriginallink.

NumberFormatInfonfi=newCultureInfo(“en-US”,false).NumberFormat; nfi.CurrencyPositivePattern=0;

nfi.CurrencyDecimalSeparator=”..”;

string.Format(nfi,”{0:C}”,112.236677);//$112..24

CustomDecimalSeparator

Section12.6:Usingcustomnumberformat

NumberFormatInfocanbeusedforformattingbothintegerandfloatnumbers.

//invariantResultis“1,234,567.89”

varinvarianResult=string.Format(CultureInfo.InvariantCulture,”{0:#,###,##}”,1234567.89);

//NumberFormatInfoisoneofclassesthatimplementIFormatProvider

varcustomProvider=newNumberFormatInfo

{

NumberDecimalSeparator=”_NS_”,//willbeusedinsteadof‘,’

NumberGroupSeparator=”_GS_”,//willbeusedinsteadof‘.’

};

//customResultis“1_GS_234_GS_567_NS_89”

varcustomResult=string.Format(customProvider,”{0:#,###.##}”,1234567.89);

Section12.7:Alignleft/right,padwithspaces

Thesecondvalueinthecurlybracesdictatesthelengthofthereplacementstring.Byadjustingthesecondvalueto be positive or negative, the alignment of the string can be changed.

string.Format(“LEFT:  string:->{0,-5}<-int:->{1,-5}<-“,”abc”,123);

string.Format(“RIGHT:string:->{0,5}<-int:->{1,5}<-“,”abc”,123);

Output:

LEFT:    string:->abc  <-int:->123           <-

RIGHT:string:->          abc<-int:->            123<-

Section12.8:Numericformats

//Integraltypesashex

string.Format(“Hexadecimal:byte2:{0:x2};byte4:{0:X4};char:{1:x2}”,123,(int)’A’);

//Integerswiththousandseparators

string.Format(“Integer,thousandsep.:{0:#,#};fixedlength:>{0,10:#,#}<“,1234567);

//Integerwithleadingzeroes

string.Format(“Integer,leadingzeroes:{0:00};”,1);

//Decimals

string.Format(“Decimal,fixedprecision:{0:0.000};aspercents:{0:0.00%}”,0.12);

Output:

Hexadecimal:byte2:7b;byte4:007B;char:41

Integer,thousandsep.:1,234,567;fixedlength:>1,234,567<Integer,lead

ingzeroes:01;

Decimal,fixedprecision:0.120;aspercents:12.00%

Section12.9:ToString()

TheToString()methodispresentonallreferenceobjecttypes.Thisisduetoallreferencetypesbeingderivedfrom Object which has the ToString() method on it. The ToString() method on the object base class returns the type name. The fragment below will print out “User” to the console.

publicclassUser

{

publicstringName{get;set; }

publicintId{get;set;}

}

…

varuser=newUser{Name=”User1″,Id=5};

Console.WriteLine(user.ToString());

However,theclassUsercanalsooverrideToString()inordertoalterthestringitreturns.Thecodefragmentbelow printsout”Id:5,Name:User1″totheconsole.

publicclassUser

{

publicstringName{get;set;}

publicintId{get;set;}

publicoverrideToString()

{

returnstring.Format(“Id:{0},Name:{1}”,Id,Name);

}

}

…

varuser=newUser{Name=”User1″,Id=5};

Console.WriteLine(user.ToString());

Section 12.10: Escaping curly brackets inside a String.Format()expression

stringoutsidetext=”Iamoutsideofbracket”;

string.Format(“{{Iaminbrackets!}}{0}”,outsidetext);

//Outputs”{Iaminbrackets!}Iamoutsideofbracket”

Section12.11:RelationshipwithToString()

WhiletheString.Format()methodiscertainlyusefulinformattingdataasstrings,itmayoftenbeabitoverkill, especiallywhendealingwithasingleobjectasseenbelow:

String.Format(“{0:C}”,money);            //yields”$42.00″

An easier approach might be to simply use the ToString()method available on all objects within C#. It supports allofthesamestandardandcustomformattingstrings,butdoesn’trequirethenecessaryparametermappingas there will only be a single argument :

money.ToString(“C”);       //yields”$42.00″

Caveats&FormattingRestrictions

Whilethisapproachmaybesimplerinsomescenarios,theToString()approachislimitedwithregardstoadding leftorrightpaddinglikeyoumightdowithintheString.Format()method:

String.Format(“{0,10:C}”,money);             //yields”                  $42.00″

InordertoaccomplishthissamebehaviorwiththeToString()method,youwouldneedtouseanothermethod like PadLeft()or PadRight()respectively :

money.ToString(“C”).PadLeft(10);          //yields”                  $42.00″