Questo articolo è stato tradotto automaticamente. Per visualizzare l'articolo in inglese, selezionare la casella di controllo Inglese. È possibile anche visualizzare il testo inglese in una finestra popup posizionando il puntatore del mouse sopra il testo.

Metodo String.IndexOf (String, Int32, Int32)


Restituisce l'indice in base zero della prima occorrenza della stringa specificata in questa istanza. La ricerca viene eseguita iniziando dalla posizione specificata dei caratteri ed esamina un determinato numero di posizioni.

Spazio dei nomi:   System
Assembly:  mscorlib (in mscorlib.dll)

public int IndexOf(
	string value,
	int startIndex,
	int count


Type: System.String

Stringa da cercare.

Type: System.Int32

Posizione iniziale della ricerca.

Type: System.Int32

Numero di posizioni dei caratteri da esaminare.

Valore restituito

Type: System.Int32

Posizione dell'indice in base zero di value dall'inizio dell'istanza corrente se la stringa viene trovata oppure -1 in caso contrario. Se value è String.Empty, il valore restituito è startIndex.

Exception Condition

value è null.


count o startIndex è negativo.


startIndex è maggiore della lunghezza di questa stringa.


count è maggiore della lunghezza di questa stringa meno startIndex.

Index numbering starts from 0 (zero). The startIndex parameter can range from 0 to the length of the string instance.

This method performs a word (case-sensitive and culture-sensitive) search using the current culture. The search begins at startIndex and continues to startIndex + count -1. The character at startIndex + count is not included in the search.

Character sets include ignorable characters, which are characters that are not considered when performing a linguistic or culture-sensitive comparison. In a culture-sensitive search, if value contains an ignorable character, the result is equivalent to searching with that character removed. If value consists only of one or more ignorable characters, the M:System.String.IndexOf(System.String,System.Int32,System.Int32) method always returns startIndex, which is the character position at which the search begins. In the following example, the M:System.String.IndexOf(System.String,System.Int32,System.Int32) method is used to find the position of a soft hyphen (U+00AD) followed by an "m" starting in the third through sixth character positions in two strings. Only one of the strings contains the required substring. If the example is run on the netfx40_short or later, in both cases, because the soft hyphen is an ignorable character, the method returns the index of "m" in the string when it performs a culture-sensitive comparison. Note that in the case of the first string, which includes the soft hyphen followed by an "m", the method fails to return the index of the soft hyphen but instead returns the index of the "m".

using System;

public class Example
   public static void Main()
      string searchString = "\u00ADm";
      string s1 = "ani\u00ADmal" ;
      string s2 = "animal";

      Console.WriteLine(s1.IndexOf(searchString, 2, 4));
      Console.WriteLine(s2.IndexOf(searchString, 2, 4));
// The example displays the following output:
//       4
//       3

Note per i chiamanti:

As explained in Best Practices for Using Strings in the .NET Framework, we recommend that you avoid calling string comparison methods that substitute default values and instead call methods that require parameters to be explicitly specified. To use the comparison rules of the current culture to perform this operation, call the M:System.String.IndexOf(System.String,System.Int32,System.Int32,System.StringComparison) method overload with a value of F:System.StringComparison.CurrentCulture for its comparisonType parameter.

The following example finds the index of all occurrences of the string "he" within a substring of another string. Note that the number of characters to be searched must be recalculated for each search iteration.

// Sample for String.IndexOf(String, Int32, Int32)
using System;

class Sample {
    public static void Main() {

    string br1 = "0----+----1----+----2----+----3----+----4----+----5----+----6----+-";
    string br2 = "0123456789012345678901234567890123456789012345678901234567890123456";
    string str = "Now is the time for all good men to come to the aid of their party.";
    int start;
    int at;
    int end;
    int count;

    end = str.Length;
    start = end/2;
    Console.WriteLine("All occurrences of 'he' from position {0} to {1}.", start, end-1);
    Console.WriteLine("{1}{0}{2}{0}{3}{0}", Environment.NewLine, br1, br2, str);
    Console.Write("The string 'he' occurs at position(s): ");

    count = 0;
    at = 0;
    while((start <= end) && (at > -1))
// start+count must be a position within -str-.
        count = end - start;
        at = str.IndexOf("he", start, count);
        if (at == -1) break;
        Console.Write("{0} ", at);
        start = at+1;
This example produces the following results:

All occurrences of 'he' from position 33 to 66.
Now is the time for all good men to come to the aid of their party.

The string 'he' occurs at position(s): 45 56


Universal Windows Platform
Disponibile da 8
.NET Framework
Disponibile da 1.1
Libreria di classi portabile
Supportato in: piattaforme .NET portabili
Disponibile da 2.0
Windows Phone Silverlight
Disponibile da 7.0
Windows Phone
Disponibile da 8.1
Torna all'inizio