Статья
11/18/2011

String.IndexOf Method (Char)

Microsoft Silverlight will reach end of support after October 2021. Learn more.

Reports the zero-based index of the first occurrence of the specified Unicode character in this string.

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

Syntax

'Declaration
Public Function IndexOf ( _
    value As Char _
) As Integer

public int IndexOf(
    char value
)

Parameters

value
Type: System.Char
A Unicode character to seek.

Return Value

Type: System.Int32
The zero-based index position of value if that character is found, or -1 if it is not.

Remarks

Index numbering starts from zero.

The search for value is case-sensitive.

This method performs an ordinal (culture-insensitive) search, where a character is considered equivalent to another character only if their Unicode scalar values are the same. To perform a culture-sensitive search, use the CompareInfo.IndexOf method, where a Unicode scalar value representing a precomposed character, such as the ligature 'Æ' (U+00C6), might be considered equivalent to any occurrence of the character's components in the correct sequence, such as "AE" (U+0041, U+0045), depending on the culture.

Examples

The following code example demonstrates how you can search a String for a character using the IndexOf method.

' Create a Unicode String with 5 Greek Alpha characters
Dim szGreekAlpha As New String(ChrW(&H319), 5)
' Create a Unicode String with a Greek Omega character
Dim szGreekOmega As New String(New Char() {ChrW(&H3A9), ChrW(&H3A9), _
                                           ChrW(&H3A9)}, 2, 1)

Dim szGreekLetters As String = String.Concat(szGreekOmega, szGreekAlpha, _
                                             szGreekOmega)

' Examine the result
outputBlock.Text &= szGreekLetters & vbCrLf

' The first index of Alpha
Dim iAlpha As Integer = szGreekLetters.IndexOf(ChrW(&H319))
' The last index of Omega
Dim iomega As Integer = szGreekLetters.LastIndexOf(ChrW(&H3A9))

outputBlock.Text &= String.Format("The Greek letter Alpha first appears at index {0}.", _
                  iAlpha) & vbCrLf
outputBlock.Text &= String.Format("The Greek letter Omega last appears at index {0}.", _
                  iomega) & vbCrLf

// Create a Unicode String with 5 Greek Alpha characters
String szGreekAlpha = new String('\u0319', 5);
// Create a Unicode String with a Greek Omega character
String szGreekOmega = new String(new char[] { '\u03A9', '\u03A9', '\u03A9' }, 2, 1);

String szGreekLetters = String.Concat(szGreekOmega, szGreekAlpha, szGreekOmega);

// Examine the result
outputBlock.Text += szGreekLetters + "\n";

// The first index of Alpha
int ialpha = szGreekLetters.IndexOf('\u0319');
// The last index of Omega
int iomega = szGreekLetters.LastIndexOf('\u03A9');

outputBlock.Text += "The Greek letter Alpha first appears at index " + ialpha +
    " and Omega last appears at index " + iomega + " in this String." + "\n";

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.

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