String.Format Method (String, array<Object>[]()[])

  • Article

[ This article is for Windows Phone 8 developers. If you’re developing for Windows 10, see the latest documentation. ]

Replaces the format item in a specified string with the string representation of a corresponding object in a specified array.

Namespace:  System
Assembly:  mscorlib (in mscorlib.dll)

Syntax

Public Shared Function Format ( _
    format As String, _
    ParamArray args As Object() _
) As String

public static string Format(
    string format,
    params Object[] args
)

Parameters

  • args
    Type: array<System..::.Object>[]()[]
    An object array that contains zero or more objects to format.

Return Value

Type: System..::.String
A copy of format in which the format items have been replaced by the string representation of the corresponding objects in args.

Exceptions

Exception Condition
ArgumentNullException

format or args is nullNothingnullptra null reference (Nothing in Visual Basic).
FormatException

format is invalid.

-or-

The index of a format item is less than zero, or greater than or equal to the length of the args array.

Remarks

This method uses the Composite Formatting of the .NET Framework to convert the value of an object to its string representation and embed that representation in a string. The .NET Framework provides extensive formatting support, which is described in greater detail in the following formatting topics in the .NET Framework documentation for desktop apps.

The format parameter consists of zero or more runs of text intermixed with zero or more indexed placeholders, called format items, that correspond to an object in the parameter list of this method. The formatting process replaces each format item with the string representation of the corresponding object.

The syntax of a format item is as follows:

{index[,length][:formatString]}

Elements in square brackets are optional. The following table describes each element. For more information about the composite formatting feature, including the syntax of a format item, see Composite Formatting.

Element

Description

index

The zero-based position in the parameter list of the object to be formatted. If the object specified by index is nullNothingnullptra null reference (Nothing in Visual Basic), the format item is replaced by String..::.Empty. If there is no parameter in the index position, a FormatException is thrown.

,length

The minimum number of characters in the string representation of the parameter. If positive, the parameter is right-aligned; if negative, it is left-aligned.

:formatString

A standard or custom format string that is supported by the object to be formatted. Possible values for formatString are the same as the values supported by the object's ToString(format) method. If formatString is not specified and the object to be formatted implements the IFormattable interface, nullNothingnullptra null reference (Nothing in Visual Basic) is passed as the value of the format parameter that is used as the IFormattable..::.ToString format string.

Note

For the standard and custom format strings used with date and time values, see Standard Date and Time Format Strings and Custom Date and Time Format Strings. For the standard and custom format strings used with numeric values, see Standard Numeric Format Strings and Custom Numeric Format Strings. For the standard format strings used with enumerations, see Enumeration Format Strings.

The leading and trailing brace characters, '{' and '}', are required. To specify a single literal brace character in format, specify two leading or trailing brace characters; that is, "{{" or "}}".

If the value of format is, "Thank you for your purchase of {0:####} copies of Microsoft®.NET (Core Reference).", and arg[0] is an Int16 with the value 123, then the return value will be:

"Thank you for your purchase of 123 copies of Microsoft®.NET (Core Reference)."

If the value of format is, "Brad's dog has {0,-8:G} fleas.", arg[0]is an Int16 with the value 42, (and in this example, underscores represent padding spaces) then the return value will be:

"Brad's dog has 42______ fleas."

Examples

The following example creates a string that contains data on the high and low temperature on a particular date. The composite format string has five format items in the C# example and six in the Visual Basic example. Two of the format items define the width of their corresponding value's string representation, and the first format item also includes a standard date and time format string.

Module Example
   Public Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)
      Dim date1 As Date = #7/1/2009#
      Dim hiTime As New TimeSpan(14, 17, 32)
      Dim hiTemp As Decimal = 62.1D
      Dim loTime As New TimeSpan(3, 16, 10)
      Dim loTemp As Decimal = 54.8D

      Dim result1 As String = String.Format("Temperature on {0:d}:{5}{1,11}: {2} degrees (hi){5}{3,11}: {4} degrees (lo)", _
                                           date1, hiTime, hiTemp, loTime, loTemp, vbCrLf)
      outputBlock.Text &= result1 & vbCrLf
      outputBlock.Text &= vbCrLf

      Dim result2 As String = String.Format("Temperature on {0:d}:{5}{1,11}: {2} degrees (hi){5}{3,11}: {4} degrees (lo)", _
                                            New Object() {date1, hiTime, hiTemp, loTime, loTemp, vbCrLf})
      outputBlock.Text &= result2 & vbCrLf
   End Sub
End Module
' The example displays the following output:
'       Temperature on 7/1/2009:
'          14:17:32: 62.1 degrees (hi)
'          03:16:10: 54.8 degrees (lo)
'
'       Temperature on 7/1/2009:
'          14:17:32: 62.1 degrees (hi)
'          03:16:10: 54.8 degrees (lo)

using System;

public class Example
{
   public static void Demo(System.Windows.Controls.TextBlock outputBlock)
   {
      DateTime date1 = new DateTime(2009, 7, 1);
      TimeSpan hiTime = new TimeSpan(14, 17, 32);
      decimal hiTemp = 62.1m;
      TimeSpan loTime = new TimeSpan(3, 16, 10);
      decimal loTemp = 54.8m;

      string result1 = String.Format("Temperature on {0:d}:\n{1,11}: {2} degrees (hi)\n{3,11}: {4} degrees (lo)",
                                     date1, hiTime, hiTemp, loTime, loTemp);
      outputBlock.Text += result1 + "\n";
      outputBlock.Text += "\n";

      string result2 = String.Format("Temperature on {0:d}:\n{1,11}: {2} degrees (hi)\n{3,11}: {4} degrees (lo)",
                                     new object[] { date1, hiTime, hiTemp, loTime, loTemp });
      outputBlock.Text += result2 + "\n";
   }
}
// The example displays the following output:
//       Temperature on 7/1/2009:
//          14:17:32: 62.1 degrees (hi)
//          03:16:10: 54.8 degrees (lo)
//       Temperature on 7/1/2009:
//          14:17:32: 62.1 degrees (hi)
//          03:16:10: 54.8 degrees (lo)

Version Information

Windows Phone OS

Supported in: 8.1, 8.0, 7.1, 7.0

Platforms

Windows Phone

See Also

Reference

String Class

Format Overload

System Namespace

Other Resources

Formatting Types

Composite Formatting

Standard Date and Time Format Strings

Custom Date and Time Format Strings

Standard Numeric Format Strings

Custom Numeric Format Strings

Standard TimeSpan Format Strings

Custom TimeSpan Format Strings

Enumeration Format Strings