Updated: December 2009
Replaces one or more format items in a specified string with the string representation of a specified object.
(in mscorlib.dll)
'Usage
Dim format As String
Dim arg0 As Object
Dim returnValue As String
returnValue = String.Format(format, _
arg0)
'Declaration
Public Shared Function Format ( _
format As String, _
arg0 As Object _
) As String
Return Value
Type:
System..::.StringA copy of format in which any format items are replaced by the string representation of arg0.
| Exception | Condition |
|---|
| ArgumentNullException |
format is nullNothingnullptra null reference (Nothing in Visual Basic). |
| FormatException | The format item in format is invalid. -or- The index of a format item is greater or less than zero. |
This method uses the composite formatting feature of the .NET Framework to convert the value of an object to its string representation and to embed that representation in a string. The .NET Framework provides extensive formatting support, which is described in greater detail in the following formatting topics.
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 value 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.
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. Because this overload has only a single object in its parameter list, the value of index must always be 0. 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 parameter. |
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 "}}".
Although the String..::.Format(String, Object) method has a single object in the parameter list, format can include more than one format item as long as each has the same index. In the following example, the format string includes two format items: one displays the decimal value of a number and the other displays its hexadecimal value.
Module Example
Public Sub Main()
Dim values() As Short = { Int16.MinValue, -27, 0, 1042, Int16.MaxValue }
Console.WriteLine("{0,10} {1,10}", "Decimal", "Hex")
Console.WriteLine()
For Each value As Short In values
Dim formatString As String = String.Format("{0,10:G}: {0,10:X}", value)
Console.WriteLine(formatString)
Next
End Sub
End Module
' The example displays the following output:
' Decimal Hex
'
' -32768: 8000
' -27: FFE5
' 0: 0
' 1042: 412
' 32767: 7FFF
If the value of format is, "Thank you for your purchase of {0:####} copies of Microsoft®.NET (Core Reference).", and arg0 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.", arg0 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."
The following example uses the Format(String, Object) method to embed an individual's age in the middle of a string.
Module Example
Public Sub Main()
Dim birthdate As Date = #7/28/1993#
Dim dates() As Date = { #9/16/1993#, #7/28/1994#, #10/16/2000#, _
#7/27/2003#, #5/27/2007# }
For Each dateValue As Date In dates
Dim interval As TimeSpan = dateValue - birthdate
' Get the approximate number of years, without accounting for leap years.
Dim years As Integer = CInt(interval.TotalDays) \ 365
' See if adding the number of years exceeds dateValue.
Dim output As String
If birthdate.AddYears(years) <= dateValue Then
output = String.Format("You are now {0} years old.", years)
Console.WriteLine(output)
Else
output = String.Format("You are now {0} years old.", years - 1)
Console.WriteLine(output)
End If
Next
End Sub
End Module
' The example displays the following output:
' You are now 0 years old.
' You are now 1 years old.
' You are now 7 years old.
' You are now 9 years old.
' You are now 13 years old.
Windows 7, Windows Vista, Windows XP SP2, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP Starter Edition, Windows Server 2008 R2, Windows Server 2008, Windows Server 2003, Windows Server 2000 SP4, Windows Millennium Edition, Windows 98, Windows CE, Windows Mobile for Smartphone, Windows Mobile for Pocket PC, Xbox 360, Zune
The .NET Framework and .NET Compact Framework do not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
.NET Framework
Supported in: 3.5, 3.0, 2.0, 1.1, 1.0
.NET Compact Framework
Supported in: 3.5, 2.0, 1.0
XNA Framework
Supported in: 3.0, 2.0, 1.0
Reference
Other Resources
Date | History | Reason |
|---|
December 2009
| Replaced the example. |
Customer feedback.
|
October 2008
| Expanded the Remarks section. |
Customer feedback.
|