String.StartsWith Method (String, StringComparison)
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Updated: October 2010
Determines whether the beginning of this string instance matches the specified string when compared using the specified comparison option.
Namespace: System
Assembly: mscorlib (in mscorlib.dll)
Syntax
'Declaration
<ComVisibleAttribute(False)> _
<SecuritySafeCriticalAttribute> _
Public Function StartsWith ( _
value As String, _
comparisonType As StringComparison _
) As Boolean
[ComVisibleAttribute(false)]
[SecuritySafeCriticalAttribute]
public bool StartsWith(
string value,
StringComparison comparisonType
)
Parameters
- value
Type: System.String
The string to compare.
- comparisonType
Type: System.StringComparison
One of the enumeration values that determines how this string and value are compared.
Return Value
Type: System.Boolean
true if the value parameter matches the beginning of this string; otherwise, false.
Exceptions
| Exception | Condition |
|---|---|
| ArgumentNullException | value is nulla null reference (Nothing in Visual Basic). |
| ArgumentException | comparisonType is not a StringComparison value. |
Remarks
The StartsWith method compares the value parameter to the substring at the beginning of this string and returns a value that indicates whether they are equal. To be equal, value must be a reference to this same string, must be the empty string (""), or must match the beginning of this string. The type of comparison performed by the StartsWith method depends on the value of the comparisonType parameter. The comparison can use the conventions of the current culture (StringComparison.CurrentCulture and StringComparison.CurrentCultureIgnoreCase) or the invariant culture (StringComparison.InvariantCulture and StringComparison.InvariantCultureIgnoreCase), or it can consist of a character-by-character comparison of code points (StringComparison.Ordinal or StringComparison.OrdinalIgnoreCase). The comparison can also be case-sensitive (StringComparison.CurrentCulture, StringComparison.InvariantCulture, or StringComparison.Ordinal), or it can ignore case (StringComparison.CurrentCultureIgnoreCase, StringComparison.InvariantCultureIgnoreCase, StringComparison.OrdinalIgnoreCase).
Platform Notes
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Silverlight for Windows Phone
The StartsWith(String, StringComparison) method returns incorrect values when the string contains Unicode characters.
Examples
The following code example determines whether a string starts with a particular substring. The results are affected by the choice of culture, whether case is ignored, and whether an ordinal comparison is performed.
' This example demonstrates the
' System.String.StartsWith(String, StringComparison) method.
Imports System.Threading
Class Example
Public Shared Sub Demo(ByVal outputBlock As System.Windows.Controls.TextBlock)
Dim intro As String = "Determine whether a string starts with another string, " & _
"using" & vbCrLf & " different values of StringComparison."
Dim scValues As StringComparison() = { _
StringComparison.CurrentCulture, _
StringComparison.CurrentCultureIgnoreCase, _
StringComparison.InvariantCulture, _
StringComparison.InvariantCultureIgnoreCase, _
StringComparison.Ordinal, _
StringComparison.OrdinalIgnoreCase}
outputBlock.Text &= intro & vbCrLf
' Display the current culture because the culture-specific comparisons
' can produce different results with different cultures.
outputBlock.Text &= String.Format("The current culture is {0}." & vbCrLf, _
Thread.CurrentThread.CurrentCulture.Name) & vbCrLf
' Determine whether three versions of the letter I are equal to each other.
Dim sc As StringComparison
For Each sc In scValues
outputBlock.Text &= String.Format("StringComparison.{0}:", sc) & vbCrLf
Test(outputBlock, "ABCxyz", "ABC", sc)
Test(outputBlock, "ABCxyz", "abc", sc)
outputBlock.Text &= vbCrLf
Next sc
End Sub 'Main
Protected Shared Sub Test(ByVal outputBlock As System.Windows.Controls.TextBlock, ByVal x As String, ByVal y As String, _
ByVal comparison As StringComparison)
Dim resultFmt As String = """{0}"" {1} with ""{2}""."
Dim result As String = "does not start"
'
If x.StartsWith(y, comparison) Then
result = "starts"
End If
outputBlock.Text &= String.Format(resultFmt, x, result, y) & vbCrLf
End Sub 'Test
End Class 'Sample
'
'This code example produces the following results:
'
'Determine whether a string starts with another string, using
' different values of StringComparison.
'The current culture is en-US.
'
'StringComparison.CurrentCulture:
'"ABCxyz" starts with "ABC".
'"ABCxyz" does not start with "abc".
'
'StringComparison.CurrentCultureIgnoreCase:
'"ABCxyz" starts with "ABC".
'"ABCxyz" starts with "abc".
'
'StringComparison.InvariantCulture:
'"ABCxyz" starts with "ABC".
'"ABCxyz" does not start with "abc".
'
'StringComparison.InvariantCultureIgnoreCase:
'"ABCxyz" starts with "ABC".
'"ABCxyz" starts with "abc".
'
'StringComparison.Ordinal:
'"ABCxyz" starts with "ABC".
'"ABCxyz" does not start with "abc".
'
'StringComparison.OrdinalIgnoreCase:
'"ABCxyz" starts with "ABC".
'"ABCxyz" starts with "abc".
'
// This example demonstrates the
// System.String.StartsWith(String, StringComparison) method.
using System;
using System.Threading;
class Example
{
public static void Demo(System.Windows.Controls.TextBlock outputBlock)
{
string intro = "Determine whether a string starts with another string, " +
"using\n different values of StringComparison.";
StringComparison[] scValues = {
StringComparison.CurrentCulture,
StringComparison.CurrentCultureIgnoreCase,
StringComparison.InvariantCulture,
StringComparison.InvariantCultureIgnoreCase,
StringComparison.Ordinal,
StringComparison.OrdinalIgnoreCase };
outputBlock.Text += intro + "\n";
// Display the current culture because the culture-specific comparisons
// can produce different results with different cultures.
outputBlock.Text += String.Format("The current culture is {0}.\n",
Thread.CurrentThread.CurrentCulture.Name) + "\n";
// Determine whether three versions of the letter I are equal to each other.
foreach (StringComparison sc in scValues)
{
outputBlock.Text += String.Format("StringComparison.{0}:", sc) + "\n";
Test(outputBlock, "ABCxyz", "ABC", sc);
Test(outputBlock, "ABCxyz", "abc", sc);
outputBlock.Text += "\n";
}
}
protected static void Test(System.Windows.Controls.TextBlock outputBlock, string x, string y, StringComparison comparison)
{
string resultFmt = "\"{0}\" {1} with \"{2}\".";
string result = "does not start";
//
if (x.StartsWith(y, comparison))
result = "starts";
outputBlock.Text += String.Format(resultFmt, x, result, y) + "\n";
}
}
/*
This code example produces the following results:
Determine whether a string starts with another string, using
different values of StringComparison.
The current culture is en-US.
StringComparison.CurrentCulture:
"ABCxyz" starts with "ABC".
"ABCxyz" does not start with "abc".
StringComparison.CurrentCultureIgnoreCase:
"ABCxyz" starts with "ABC".
"ABCxyz" starts with "abc".
StringComparison.InvariantCulture:
"ABCxyz" starts with "ABC".
"ABCxyz" does not start with "abc".
StringComparison.InvariantCultureIgnoreCase:
"ABCxyz" starts with "ABC".
"ABCxyz" starts with "abc".
StringComparison.Ordinal:
"ABCxyz" starts with "ABC".
"ABCxyz" does not start with "abc".
StringComparison.OrdinalIgnoreCase:
"ABCxyz" starts with "ABC".
"ABCxyz" starts with "abc".
*/
Version Information
Silverlight
Supported in: 5, 4, 3
Silverlight for Windows Phone
Supported in: Windows Phone OS 7.1, Windows Phone OS 7.0
XNA Framework
Supported in: Xbox 360, Windows Phone OS 7.0
Platforms
For a list of the operating systems and browsers that are supported by Silverlight, see Supported Operating Systems and Browsers.
Change History
Date |
History |
Reason |
|---|---|---|
October 2010 |
Expanded the Remarks section and replaced the example. |
Customer feedback. |