String.IndexOf Method (Char, Int32, Int32)
[ This article is for Windows Phone 8 developers. If you’re developing for Windows 10, see the latest documentation. ]
Reports the zero-based index of the first occurrence of the specified character in this instance. The search starts at a specified character position and examines a specified number of character positions.
Assembly: mscorlib (in mscorlib.dll)
Parameters
- value
- Type: System.Char
A Unicode character to seek.
- startIndex
- Type: System.Int32
The search starting position.
- count
- Type: System.Int32
The number of character positions to examine.
Return Value
Type: System.Int32The zero-based index position of value if that character is found, or -1 if it is not.
| Exception | Condition |
|---|---|
| ArgumentOutOfRangeException | count or startIndex is negative. -or- startIndex is greater than the length of this string. -or- count is greater than the length of this string minus startIndex. |
The search begins at startIndex and continues to startIndex + count -1. The character at startIndex + count is not included in the search.
Index numbering starts from zero. startIndex can range from 0 to the length of the string instance.
This method performs an ordinal (culture-insensitive, case-sensitive) search, where a character is considered equivalent to another character only if their Unicode scalar value 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.
The following example demonstrates the IndexOf method.
// Example for the String.IndexOf( char, int, int ) method. using System; class Example { public static void Demo(System.Windows.Controls.TextBlock outputBlock) { string br1 = "0----+----1----+----2----+----3----+----" + "4----+----5----+----6----+----7"; string br2 = "0123456789012345678901234567890123456789" + "0123456789012345678901234567890"; string str = "ABCDEFGHI abcdefghi ABCDEFGHI abcdefghi " + "ABCDEFGHI abcdefghi ABCDEFGHI"; outputBlock.Text += "This example of String.IndexOf( char, int, int )\n" + "generates the following output." + "\n"; outputBlock.Text += String.Format( "{0}{1}{0}{2}{0}{3}{0}", Environment.NewLine, br1, br2, str) + "\n"; FindAllChar(outputBlock, 'A', str); FindAllChar(outputBlock, 'a', str); FindAllChar(outputBlock, 'I', str); FindAllChar(outputBlock, 'i', str); FindAllChar(outputBlock, '@', str); FindAllChar(outputBlock, ' ', str); } static void FindAllChar(System.Windows.Controls.TextBlock outputBlock, Char target, String searched) { outputBlock.Text += String.Format( "The character '{0}' occurs at position(s): ", target); int startIndex = -1; int hitCount = 0; // Search for all occurrences of the target. while (true) { startIndex = searched.IndexOf( target, startIndex + 1, searched.Length - startIndex - 1); // Exit the loop if the target is not found. if (startIndex < 0) break; outputBlock.Text += String.Format("{0}, ", startIndex); hitCount++; } outputBlock.Text += String.Format("occurrences: {0}", hitCount) + "\n"; } } /* This example of String.IndexOf( char, int, int ) generates the following output. 0----+----1----+----2----+----3----+----4----+----5----+----6----+----7 01234567890123456789012345678901234567890123456789012345678901234567890 ABCDEFGHI abcdefghi ABCDEFGHI abcdefghi ABCDEFGHI abcdefghi ABCDEFGHI The character 'A' occurs at position(s): 0, 20, 40, 60, occurrences: 4 The character 'a' occurs at position(s): 10, 30, 50, occurrences: 3 The character 'I' occurs at position(s): 8, 28, 48, 68, occurrences: 4 The character 'i' occurs at position(s): 18, 38, 58, occurrences: 3 The character '@' occurs at position(s): occurrences: 0 The character ' ' occurs at position(s): 9, 19, 29, 39, 49, 59, occurrences: 6 */