Array.FindIndex<T> Method (T[], Int32, Int32, Predicate<T>)

Searches for an element that matches the conditions defined by the specified predicate, and returns the zero-based index of the first occurrence within the range of elements in the Array that starts at the specified index and contains the specified number of elements.

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

public static int FindIndex<T>(
	T[] array,
	int startIndex,
	int count,
	Predicate<T> match
)

Type Parameters

T

The type of the elements of the array.

Parameters

array
Type: T[]
The one-dimensional, zero-based Array to search.
startIndex
Type: System.Int32
The zero-based starting index of the search.
count
Type: System.Int32
The number of elements in the section to search.
match
Type: System.Predicate<T>
The Predicate<T> that defines the conditions of the element to search for.

Return Value

Type: System.Int32
The zero-based index of the first occurrence of an element that matches the conditions defined by match, if found; otherwise, –1.

ExceptionCondition
ArgumentNullException

array is null.

-or-

match is null.

ArgumentOutOfRangeException

startIndex is outside the range of valid indexes for array.

-or-

count is less than zero.

-or-

startIndex and count do not specify a valid section in array.

The Array is searched forward starting at startIndex and ending at startIndex plus count minus 1, if count is greater than 0.

The Predicate<T> is a delegate to a method that returns true if the object passed to it matches the conditions defined in the delegate. The elements of array are individually passed to the Predicate<T>.

This method is an O(n) operation, where n is count.

The following code example demonstrates all three overloads of the FindIndex generic method. An array of strings is created, containing 8 dinosaur names, two of which (at positions 1 and 5) end with "saurus". The code example also defines a search predicate method named EndsWithSaurus, which accepts a string parameter and returns a Boolean value indicating whether the input string ends in "saurus".

The FindIndex<T>(T[], Predicate<T>) method overload traverses the array from the beginning, passing each element in turn to the EndsWithSaurus method. The search stops when the EndsWithSaurus method returns true for the element at position 1.

NoteNote

In C# and Visual Basic, it is not necessary to create the Predicate<string> delegate (Predicate(Of String) in Visual Basic) explicitly. These languages infer the correct delegate from context and create it automatically.

The FindIndex<T>(T[], Int32, Predicate<T>) method overload is used to search the array beginning at position 2 and continuing to the end of the array. It finds the element at position 5. Finally, the FindIndex<T>(T[], Int32, Int32, Predicate<T>) method overload is used to search the range of three elements beginning at position 2. It returns –1 because there are no dinosaur names in that range that end with "saurus".


using System;

public class Example
{
    public static void Main()
    {
        string[] dinosaurs = { "Compsognathus", 
            "Amargasaurus",   "Oviraptor",      "Velociraptor", 
            "Deinonychus",    "Dilophosaurus",  "Gallimimus", 
            "Triceratops" };

        Console.WriteLine();
        foreach(string dinosaur in dinosaurs)
        {
            Console.WriteLine(dinosaur);
        }

        Console.WriteLine(
            "\nArray.FindIndex(dinosaurs, EndsWithSaurus): {0}", 
            Array.FindIndex(dinosaurs, EndsWithSaurus));

        Console.WriteLine(
            "\nArray.FindIndex(dinosaurs, 2, EndsWithSaurus): {0}",
            Array.FindIndex(dinosaurs, 2, EndsWithSaurus));

        Console.WriteLine(
            "\nArray.FindIndex(dinosaurs, 2, 3, EndsWithSaurus): {0}",
            Array.FindIndex(dinosaurs, 2, 3, EndsWithSaurus));
    }

    // Search predicate returns true if a string ends in "saurus".
    private static bool EndsWithSaurus(String s)
    {
        if ((s.Length > 5) && 
            (s.Substring(s.Length - 6).ToLower() == "saurus"))
        {
            return true;
        }
        else
        {
            return false;
        }
    }
}

/* This code example produces the following output:

Compsognathus
Amargasaurus
Oviraptor
Velociraptor
Deinonychus
Dilophosaurus
Gallimimus
Triceratops

Array.FindIndex(dinosaurs, EndsWithSaurus): 1

Array.FindIndex(dinosaurs, 2, EndsWithSaurus): 5

Array.FindIndex(dinosaurs, 2, 3, EndsWithSaurus): -1
 */


.NET Framework

Supported in: 4, 3.5, 3.0, 2.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows XP SP2 x64 Edition, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
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