Chapter 12: String.Format

The Format methods are a set of overloads in the System.String class used to create strings that combine objects

into specific string representations. This information can be applied to String.Format, various WriteLine methods as well as other methods in the .NET framework.

Section 12.1: Since C# 6.0

Version ≥ 6.0

Since C# 6.0 it is possible to use string interpolation in place of String.Format.

string name = "John"; string lastname = "Doe";

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

Hello John Doe!

More examples for this under the topic C# 6.0 features: String interpolation.

Section 12.2: Places where String.Format is 'embedded' in the framework

There are several places where you can use String.Format indirectly: The secret is to look for the overload with the signature string format, params object[] args, e.g.:

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

Can be replaced with shorter version:

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

There are other methods which also use String.Formate.g.:

Debug.WriteLine(); // and Print()

StringBuilder.AppendFormat();

Section 12.3: Create a custom format provider

public class CustomFormat : IFormatProvider, ICustomFormatter

{

public string Format(string format, object arg, IFormatProvider formatProvider)

{

if (!this.Equals(formatProvider))

{

return null;

}

if (format == "Reverse")

{

return String.Join("", arg.ToString().Reverse());

}

return arg.ToString();

}

public object GetFormat(Type formatType)

{

return formatType==typeof(ICustomFormatter) ? this:null;

}

}

Usage:

String.Format(new CustomFormat(), "-> {0:Reverse} <-", "Hello World");

Output:

-> dlroW olleH <-

Section 12.4: Date Formatting

DateTime date = new DateTime(2016, 07, 06, 18, 30, 14);

// Format: year, month, day hours, minutes, seconds

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

//Format by Culture info

String.Format(new System.Globalization.CultureInfo("mn-MN"),"{0:dddd}",date);

Version ≥ 6.0

Console.Write($"{date:ddd}");

output :

06

Лхагва

06

Section 12.5: Currency Formatting

The "c" (or currency) format specifier converts a number to a string that represents a currency amount. string.Format("{0:c}", 112.236677) // $112.23 - defaults to system

Precision

Default is 2. Use c1, c2, c3 and so on to control precision.

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

Currency Symbol

1. Pass CultureInfo instance to use custom culture symbol.

string.Format(new CultureInfo("en-US"), "{0:c}", 112.236677); //$112.24 string.Format(new CultureInfo("de-DE"), "{0:c}", 112.236677); //112,24 € string.Format(new CultureInfo("hi-IN"), "{0:c}", 112.236677); // 112.24

2. Use any string as currency symbol. Use NumberFormatInfo as to customize currency symbol.

NumberFormatInfo nfi = new CultureInfo( "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

Position of Currency Symbol

Use CurrencyPositivePattern for positive values and CurrencyNegativePattern for negative values.

NumberFormatInfo nfi = new CultureInfo( "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 $

Negative pattern usage is the same as positive pattern. A lot more use cases please refer to original link.

Custom Decimal Separator

NumberFormatInfo nfi = new CultureInfo( "en-US", false ).NumberFormat; nfi.CurrencyPositivePattern = 0;

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

Section 12.6: Using custom number format

NumberFormatInfo can be used for formatting both integer and float numbers.

// invariantResult is "1,234,567.89"

var invarianResult = string.Format(CultureInfo.InvariantCulture, "{0:#,###,##}", 1234567.89);

//NumberFormatInfo is one of classes that implement IFormatProvider var customProvider = new NumberFormatInfo

{

NumberDecimalSeparator = "_NS_", // will be used instead of ',' NumberGroupSeparator = "_GS_", // will be used instead of '.'

};

//customResult is "1_GS_234_GS_567_NS_89"

var customResult = string.Format(customProvider, "{0:#,###.##}", 1234567.89);

Section 12.7: Align left/ right, pad with spaces

The second value in the curly braces dictates the length of the replacement string. By adjusting the second value to 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<-