String.IndexOf Method (String, Int32, Int32, StringComparison)
[ 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 string in the current String object. Parameters specify the starting search position in the current string, the number of characters in the current string to search, and the type of search to use for the specified string.
Assembly: mscorlib (in mscorlib.dll)
Parameters
- value
- Type: System.String
The string to seek.
- startIndex
- Type: System.Int32
The search starting position.
- count
- Type: System.Int32
The number of character positions to examine.
- comparisonType
- Type: System.StringComparison
One of the enumeration values that specifies the rules for the search.
Return Value
Type: System.Int32The zero-based index position of the value parameter if that string is found, or -1 if it is not. If value is Empty, the return value is startIndex.
| Exception | Condition |
|---|---|
| ArgumentNullException | value is null. |
| ArgumentOutOfRangeException | count or startIndex is negative. -or- startIndex is greater than the length of this instance. -or- count is greater than the length of this string minus startIndex. |
| ArgumentException | comparisonType is not a valid System.StringComparison value. |
Index numbering starts from zero. startIndex can range from 0 to the length of the string instance.
The search begins at startIndex and continues to startIndex + count -1. The character at startIndex + count is not included in the search.
The comparisonType parameter specifies to search for the value parameter using the current or invariant culture, using a case-sensitive or case-insensitive search, and using word or ordinal comparison rules.
The following code example demonstrates three overloads of the IndexOf method that find the first occurrence of a string within another string using different values of the StringComparison enumeration.
// This code example demonstrates the // System.String.IndexOf(String, ..., StringComparison) methods. using System; using System.Threading; using System.Globalization; class Example { public static void Demo(System.Windows.Controls.TextBlock outputBlock) { string intro = "Find the first occurrence of a character using different " + "values of StringComparison."; string resultFmt = "Comparison: {0,-28} Location: {1,3}"; // Define a string to search for. // U+00c5 = LATIN CAPITAL LETTER A WITH RING ABOVE string CapitalAWithRing = "\u00c5"; // Define a string to search. // The result of combining the characters LATIN SMALL LETTER A and COMBINING // RING ABOVE (U+0061, U+030a) is linguistically equivalent to the character // LATIN SMALL LETTER A WITH RING ABOVE (U+00e5). string cat = "A Cheshire c" + "\u0061\u030a" + "t"; int loc = 0; StringComparison[] scValues = { StringComparison.CurrentCulture, StringComparison.CurrentCultureIgnoreCase, StringComparison.InvariantCulture, StringComparison.InvariantCultureIgnoreCase, StringComparison.Ordinal, StringComparison.OrdinalIgnoreCase }; // Display an introduction. outputBlock.Text += intro + "\n"; // Display the current culture because culture affects the result. For example, // try this code example with the "sv-SE" (Swedish-Sweden) culture. Thread.CurrentThread.CurrentCulture = new CultureInfo("en-US"); outputBlock.Text += String.Format("The current culture is \"{0}\" - {1}.", Thread.CurrentThread.CurrentCulture.Name, Thread.CurrentThread.CurrentCulture.DisplayName) + "\n"; // Display the string to search for and the string to search. outputBlock.Text += String.Format("Search for the string \"{0}\" in the string \"{1}\"", CapitalAWithRing, cat) + "\n"; outputBlock.Text += "\n"; // Note that in each of the following searches, we look for // LATIN CAPITAL LETTER A WITH RING ABOVE in a string that contains // LATIN SMALL LETTER A WITH RING ABOVE. A result value of -1 indicates // the string was not found. // Search using different values of StringComparison. Specify the start // index and count. outputBlock.Text += "Part 1: Start index and count are specified." + "\n"; foreach (StringComparison sc in scValues) { loc = cat.IndexOf(CapitalAWithRing, 0, cat.Length, sc); outputBlock.Text += String.Format(resultFmt, sc, loc) + "\n"; } // Search using different values of StringComparison. Specify the // start index. outputBlock.Text += "\nPart 2: Start index is specified." + "\n"; foreach (StringComparison sc in scValues) { loc = cat.IndexOf(CapitalAWithRing, 0, sc); outputBlock.Text += String.Format(resultFmt, sc, loc) + "\n"; } // Search using different values of StringComparison. outputBlock.Text += "\nPart 3: Neither start index nor count is specified." + "\n"; foreach (StringComparison sc in scValues) { loc = cat.IndexOf(CapitalAWithRing, sc); outputBlock.Text += String.Format(resultFmt, sc, loc) + "\n"; } } } /* Note: This code example was executed on a console whose user interface culture is "en-US" (English-United States). This code example produces the following results: Find the first occurrence of a character using different values of StringComparison. The current culture is "en-US" - English (United States). Search for the string "Å" in the string "A Cheshire ca°t" Part 1: Start index and count are specified. Comparison: CurrentCulture Location: -1 Comparison: CurrentCultureIgnoreCase Location: 12 Comparison: InvariantCulture Location: -1 Comparison: InvariantCultureIgnoreCase Location: 12 Comparison: Ordinal Location: -1 Comparison: OrdinalIgnoreCase Location: -1 Part 2: Start index is specified. Comparison: CurrentCulture Location: -1 Comparison: CurrentCultureIgnoreCase Location: 12 Comparison: InvariantCulture Location: -1 Comparison: InvariantCultureIgnoreCase Location: 12 Comparison: Ordinal Location: -1 Comparison: OrdinalIgnoreCase Location: -1 Part 3: Neither start index nor count is specified. Comparison: CurrentCulture Location: -1 Comparison: CurrentCultureIgnoreCase Location: 12 Comparison: InvariantCulture Location: -1 Comparison: InvariantCultureIgnoreCase Location: 12 Comparison: Ordinal Location: -1 Comparison: OrdinalIgnoreCase Location: -1 */