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String.StartsWith Metodo

  • Riferimento

Definizione

Spazio dei nomi:
System
Assembly:
System.Runtime.dll
Assembly:
mscorlib.dll
Assembly:
netstandard.dll

Overload

StartsWith(String, Boolean, CultureInfo)

Determina se l'inizio di questa istanza di stringa corrisponde alla stringa specificata se confrontata mediante le impostazioni cultura specificate.
StartsWith(String, StringComparison)

Determina se l'inizio di questa istanza di stringa corrisponde alla stringa specificata se confrontata usando l'opzione di confronto specificata.
StartsWith(Char)

Determina se questa istanza di stringa inizia con il carattere specificato.
StartsWith(String)

Determina se l'inizio di questa istanza di stringa corrisponde alla stringa specificata.

StartsWith(String, Boolean, CultureInfo)

Origine:
String.Comparison.cs
Origine:
String.Comparison.cs
Origine:
String.Comparison.cs

Determina se l'inizio di questa istanza di stringa corrisponde alla stringa specificata se confrontata mediante le impostazioni cultura specificate.

public:
 bool StartsWith(System::String ^ value, bool ignoreCase, System::Globalization::CultureInfo ^ culture);
public bool StartsWith (string value, bool ignoreCase, System.Globalization.CultureInfo? culture);
public bool StartsWith (string value, bool ignoreCase, System.Globalization.CultureInfo culture);
member this.StartsWith : string * bool * System.Globalization.CultureInfo -> bool
Public Function StartsWith (value As String, ignoreCase As Boolean, culture As CultureInfo) As Boolean

Parametri

value
String

Stringa da confrontare.

ignoreCase
Boolean

true per ignorare la distinzione tra maiuscole e minuscole durante il confronto; in caso contrario, false.

culture
CultureInfo

Informazioni relative alle impostazioni cultura che determinano le modalità di confronto fra questa stringa e il parametro value. Se culture è null, verranno usate le impostazioni cultura correnti.

Restituisce

Boolean

true se il parametro value corrisponde all'inizio di questa stringa; in caso contrario, false.

Eccezioni

ArgumentNullException

value è null.

Esempio

Nell'esempio seguente viene determinato se una stringa si verifica all'inizio di un'altra stringa. Il StartsWith metodo viene chiamato più volte usando distinzione tra maiuscole e minuscole, senza distinzione tra maiuscole e minuscole e impostazioni cultura diverse che influenzano i risultati della ricerca.

// This code example demonstrates the 
// System.String.StartsWith(String, ..., CultureInfo) method.

using System;
using System.Threading;
using System.Globalization;

class Sample 
{
    public static void Main() 
    {
    string msg1 = "Search for the target string \"{0}\" in the string \"{1}\".\n";
    string msg2 = "Using the {0} - \"{1}\" culture:";
    string msg3 = "  The string to search ends with the target string: {0}";
    bool result = false;
    CultureInfo ci;

// Define a target string to search for.
// U+00c5 = LATIN CAPITAL LETTER A WITH RING ABOVE
    string capitalARing = "\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 aRingXYZ = "\u0061\u030a" + "xyz";

// Clear the screen and display an introduction.
    Console.Clear();

// Display the string to search for and the string to search.
    Console.WriteLine(msg1, capitalARing, aRingXYZ);

// Search using English-United States culture.
    ci = new CultureInfo("en-US");
    Console.WriteLine(msg2, ci.DisplayName, ci.Name);

    Console.WriteLine("Case sensitive:");
    result = aRingXYZ.StartsWith(capitalARing, false, ci);
    Console.WriteLine(msg3, result);

    Console.WriteLine("Case insensitive:");
    result = aRingXYZ.StartsWith(capitalARing, true, ci);
    Console.WriteLine(msg3, result);
    Console.WriteLine();

// Search using Swedish-Sweden culture.
    ci = new CultureInfo("sv-SE");
    Console.WriteLine(msg2, ci.DisplayName, ci.Name);

    Console.WriteLine("Case sensitive:");
    result = aRingXYZ.StartsWith(capitalARing, false, ci);
    Console.WriteLine(msg3, result);

    Console.WriteLine("Case insensitive:");
    result = aRingXYZ.StartsWith(capitalARing, true, ci);
    Console.WriteLine(msg3, result);
    }
}

/*
Note: This code example was executed on a console whose user interface 
culture is "en-US" (English-United States).

Search for the target string "Å" in the string "a°xyz".

Using the English (United States) - "en-US" culture:
Case sensitive:
  The string to search ends with the target string: False
Case insensitive:
  The string to search ends with the target string: True

Using the Swedish (Sweden) - "sv-SE" culture:
Case sensitive:
  The string to search ends with the target string: False
Case insensitive:
  The string to search ends with the target string: False

*/

// This code example demonstrates the
// System.String.StartsWith(String, ..., CultureInfo) method.

open System
open System.Globalization
 
[<EntryPoint>]
let main _ =
    let msg1 = "Search for the target string \"{0}\" in the string \"{1}\".\n"
    let msg2 = "Using the {0} - \"{1}\" culture:"
    let msg3 = "  The string to search ends with the target string: {0}"

    // Define a target string to search for.
    // U+00c5 = LATIN CAPITAL LETTER A WITH RING ABOVE
    let capitalARing = "\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).
    let aRingXYZ = "\u0061\u030a" + "xyz"

    // Clear the screen and display an introduction.
    Console.Clear()

    // Display the string to search for and the string to search.
    Console.WriteLine(msg1, capitalARing, aRingXYZ)

    // Search using English-United States culture.
    let ci = CultureInfo "en-US"
    Console.WriteLine(msg2, ci.DisplayName, ci.Name)

    printfn "Case sensitive:"
    let result = aRingXYZ.StartsWith(capitalARing, false, ci)
    Console.WriteLine(msg3, result)

    printfn "Case insensitive:"
    let result = aRingXYZ.StartsWith(capitalARing, true, ci)
    Console.WriteLine(msg3, result)
    printfn ""

    // Search using Swedish-Sweden culture.
    let ci = CultureInfo "sv-SE"
    Console.WriteLine(msg2, ci.DisplayName, ci.Name)

    printfn "Case sensitive:"
    let result = aRingXYZ.StartsWith(capitalARing, false, ci)
    Console.WriteLine(msg3, result)

    printfn "Case insensitive:"
    let result = aRingXYZ.StartsWith(capitalARing, true, ci)
    Console.WriteLine(msg3, result)
    0
(*
Note: This code example was executed on a console whose user interface
culture is "en-US" (English-United States).

Search for the target string "Å" in the string "a°xyz".

Using the English (United States) - "en-US" culture:
Case sensitive:
  The string to search ends with the target string: False
Case insensitive:
  The string to search ends with the target string: True

Using the Swedish (Sweden) - "sv-SE" culture:
Case sensitive:
  The string to search ends with the target string: False
Case insensitive:
  The string to search ends with the target string: False

*)

' This code example demonstrates the 
' System.String.StartsWith(String, ..., CultureInfo) method.

Imports System.Threading
Imports System.Globalization

Class Sample
    Public Shared Sub Main() 
        Dim msg1 As String = "Search for the target string ""{0}"" in the string ""{1}""." & vbCrLf
        Dim msg2 As String = "Using the {0} - ""{1}"" culture:"
        Dim msg3 As String = "  The string to search ends with the target string: {0}"
        Dim result As Boolean = False
        Dim ci As CultureInfo
        
        ' Define a target string to search for.
        ' U+00c5 = LATIN CAPITAL LETTER A WITH RING ABOVE
        Dim capitalARing As String = "Å"
        
        ' 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).
        Dim aRingXYZ As String = "å" & "xyz"
        
        ' Clear the screen and display an introduction.
        Console.Clear()
        
        ' Display the string to search for and the string to search.
        Console.WriteLine(msg1, capitalARing, aRingXYZ)
        
        ' Search using English-United States culture.
        ci = New CultureInfo("en-US")
        Console.WriteLine(msg2, ci.DisplayName, ci.Name)
        
        Console.WriteLine("Case sensitive:")
        result = aRingXYZ.StartsWith(capitalARing, False, ci)
        Console.WriteLine(msg3, result)
        
        Console.WriteLine("Case insensitive:")
        result = aRingXYZ.StartsWith(capitalARing, True, ci)
        Console.WriteLine(msg3, result)
        Console.WriteLine()
        
        ' Search using Swedish-Sweden culture.
        ci = New CultureInfo("sv-SE")
        Console.WriteLine(msg2, ci.DisplayName, ci.Name)
        
        Console.WriteLine("Case sensitive:")
        result = aRingXYZ.StartsWith(capitalARing, False, ci)
        Console.WriteLine(msg3, result)
        
        Console.WriteLine("Case insensitive:")
        result = aRingXYZ.StartsWith(capitalARing, True, ci)
        Console.WriteLine(msg3, result)
    
    End Sub
End Class

'
'Note: This code example was executed on a console whose user interface 
'culture is "en-US" (English-United States).
'
'Search for the target string "Å" in the string "a°xyz".
'
'Using the English (United States) - "en-US" culture:
'Case sensitive:
'  The string to search ends with the target string: False
'Case insensitive:
'  The string to search ends with the target string: True
'
'Using the Swedish (Sweden) - "sv-SE" culture:
'Case sensitive:
'  The string to search ends with the target string: False
'Case insensitive:
'  The string to search ends with the target string: False
'

Commenti

Questo metodo confronta il value parametro con la sottostringa all'inizio di questa stringa con la stessa lunghezza valuedi e restituisce un valore che indica se sono uguali. Per essere uguale, value deve essere una stringa vuota (String.Empty), deve essere un riferimento a questa stessa istanza oppure deve corrispondere all'inizio di questa istanza.

Questo metodo esegue un confronto usando le maiuscole e le impostazioni cultura specificate.

Si applica a

StartsWith(String, StringComparison)

Origine:
String.Comparison.cs
Origine:
String.Comparison.cs
Origine:
String.Comparison.cs

Determina se l'inizio di questa istanza di stringa corrisponde alla stringa specificata se confrontata usando l'opzione di confronto specificata.

public:
 bool StartsWith(System::String ^ value, StringComparison comparisonType);
public bool StartsWith (string value, StringComparison comparisonType);
[System.Runtime.InteropServices.ComVisible(false)]
public bool StartsWith (string value, StringComparison comparisonType);
member this.StartsWith : string * StringComparison -> bool
[<System.Runtime.InteropServices.ComVisible(false)>]
member this.StartsWith : string * StringComparison -> bool
Public Function StartsWith (value As String, comparisonType As StringComparison) As Boolean

Parametri

value
String

Stringa da confrontare.

comparisonType
StringComparison

Uno dei valori di enumerazione che determina la modalità di confronto fra questa stringa e value.

Restituisce

Boolean

true se l'istanza inizia con value; in caso contrario, false.

Attributi
ComVisibleAttribute

Eccezioni

ArgumentNullException

value è null.

ArgumentException

comparisonType non è un valore di StringComparison.

Esempio

Nell'esempio seguente viene cercata la stringa "the" all'inizio di una stringa più lunga che inizia con la parola "The". Come illustrato nell'output dell'esempio, una chiamata al StartsWith(String, StringComparison) metodo che esegue un confronto senza distinzione tra maiuscole e minuscole ma senza distinzione tra maiuscole e minuscole non corrisponde alla stringa, mentre una chiamata che esegue un confronto con impostazioni cultura e senza distinzione tra maiuscole e minuscole corrisponde alla stringa.

using namespace System;

void main()
{
   String^ title = "The House of the Seven Gables";
   String^ searchString = "the";
   StringComparison comparison = StringComparison::InvariantCulture;
   Console::WriteLine("'{0}':", title);
   Console::WriteLine("   Starts with '{0}' ({1:G} comparison): {2}",
                      searchString, comparison,
                      title->StartsWith(searchString, comparison));

   comparison = StringComparison::InvariantCultureIgnoreCase;
   Console::WriteLine("   Starts with '{0}' ({1:G} comparison): {2}",
                      searchString, comparison,
                      title->StartsWith(searchString, comparison));
   }
// The example displays the following output:
//       'The House of the Seven Gables':
//          Starts with 'the' (InvariantCulture comparison): False
//          Starts with 'the' (InvariantCultureIgnoreCase comparison): True

using System;

public class Example
{
   public static void Main()
   {
      String title = "The House of the Seven Gables";
      String searchString = "the";
      StringComparison comparison = StringComparison.InvariantCulture;
      Console.WriteLine("'{0}':", title);
      Console.WriteLine("   Starts with '{0}' ({1:G} comparison): {2}",
                        searchString, comparison,
                        title.StartsWith(searchString, comparison));

      comparison = StringComparison.InvariantCultureIgnoreCase;
      Console.WriteLine("   Starts with '{0}' ({1:G} comparison): {2}",
                        searchString, comparison,
                        title.StartsWith(searchString, comparison));
   }
}
// The example displays the following output:
//       'The House of the Seven Gables':
//          Starts with 'the' (InvariantCulture comparison): False
//          Starts with 'the' (InvariantCultureIgnoreCase comparison): True

open System

let title = "The House of the Seven Gables"
let searchString = "the"
let comparison = StringComparison.InvariantCulture
printfn $"'{title}':"
printfn $"   Starts with '{searchString}' ({comparison:G} comparison): {title.StartsWith(searchString, comparison)}"

let comparison2 = StringComparison.InvariantCultureIgnoreCase
printfn $"   Starts with '{searchString}' ({comparison2:G} comparison): {title.StartsWith(searchString, comparison2)}"
// The example displays the following output:
//       'The House of the Seven Gables':
//          Starts with 'the' (InvariantCulture comparison): False
//          Starts with 'the' (InvariantCultureIgnoreCase comparison): True

Module Example
   Public Sub Main()
      Dim title As String = "The House of the Seven Gables"
      Dim searchString As String = "the"
      Dim comparison As StringComparison = StringComparison.InvariantCulture
      Console.WriteLine("'{0}':", title)
      Console.WriteLine("   Starts with '{0}' ({1:G} comparison): {2}",
                        searchString, comparison,
                        title.StartsWith(searchString, comparison))

      comparison = StringComparison.InvariantCultureIgnoreCase
      Console.WriteLine("   Starts with '{0}' ({1:G} comparison): {2}",
                        searchString, comparison,
                        title.StartsWith(searchString, comparison))
   End Sub
End Module
' The example displays the following output:
'    'The House of the Seven Gables':
'       Starts with 'the' (InvariantCulture comparison): False
'       Starts with 'the' (InvariantCultureIgnoreCase comparison): True

Nell'esempio seguente viene determinato se una stringa inizia con una determinata sottostringa. Inizializza una matrice di stringhe bidimensionale. Il primo elemento nella seconda dimensione contiene una stringa e il secondo elemento contiene la stringa da cercare all'inizio della prima stringa. I risultati sono interessati dalla scelta delle impostazioni cultura, dal fatto che la distinzione tra maiuscole e minuscole venga ignorata e dal fatto che venga eseguito un confronto ordinale. Si noti che quando l'istanza di stringa contiene una legatura, i confronti con distinzione tra le impostazioni cultura e i caratteri consecutivi corrispondono correttamente.

using namespace System;

void main()
{
   array<String^, 2>^ strings = gcnew array<String^, 2> { {"ABCdef", "abc" },                    
                         {"ABCdef", "abc" }, {"œil","oe" }, 
                         { "læring}", "lae" } };
   for (int ctr1 = strings->GetLowerBound(0); ctr1 <= strings->GetUpperBound(0); ctr1++)
   {
         for each (String^ cmpName in Enum::GetNames(StringComparison::typeid))
         { 
            StringComparison strCmp = (StringComparison) Enum::Parse(StringComparison::typeid, 
                                                         cmpName);
            String^ instance = strings[ctr1, 0];
            String^ value = strings[ctr1, 1];
            Console::WriteLine("{0} starts with {1}: {2} ({3} comparison)", 
                               instance, value, 
                               instance->StartsWith(value, strCmp), 
                               strCmp); 
         }
         Console::WriteLine();   
   }   
}

// The example displays the following output:
//       ABCdef starts with abc: False (CurrentCulture comparison)
//       ABCdef starts with abc: True (CurrentCultureIgnoreCase comparison)
//       ABCdef starts with abc: False (InvariantCulture comparison)
//       ABCdef starts with abc: True (InvariantCultureIgnoreCase comparison)
//       ABCdef starts with abc: False (Ordinal comparison)
//       ABCdef starts with abc: True (OrdinalIgnoreCase comparison)
//       
//       ABCdef starts with abc: False (CurrentCulture comparison)
//       ABCdef starts with abc: True (CurrentCultureIgnoreCase comparison)
//       ABCdef starts with abc: False (InvariantCulture comparison)
//       ABCdef starts with abc: True (InvariantCultureIgnoreCase comparison)
//       ABCdef starts with abc: False (Ordinal comparison)
//       ABCdef starts with abc: True (OrdinalIgnoreCase comparison)
//       
//       œil starts with oe: True (CurrentCulture comparison)
//       œil starts with oe: True (CurrentCultureIgnoreCase comparison)
//       œil starts with oe: True (InvariantCulture comparison)
//       œil starts with oe: True (InvariantCultureIgnoreCase comparison)
//       œil starts with oe: False (Ordinal comparison)
//       œil starts with oe: False (OrdinalIgnoreCase comparison)
//       
//       læring} starts with lae: True (CurrentCulture comparison)
//       læring} starts with lae: True (CurrentCultureIgnoreCase comparison)
//       læring} starts with lae: True (InvariantCulture comparison)
//       læring} starts with lae: True (InvariantCultureIgnoreCase comparison)
//       læring} starts with lae: False (Ordinal comparison)
//       læring} starts with lae: False (OrdinalIgnoreCase comparison)

using System;

public class Example
{
   public static void Main()
   {
      string[,] strings = { {"ABCdef", "abc" },                    
                            {"ABCdef", "abc" },  
                            {"œil","oe" },
                            { "læring}", "lae" } };
      for (int ctr1 = strings.GetLowerBound(0); ctr1 <= strings.GetUpperBound(0); ctr1++)
      {
            foreach (string cmpName in Enum.GetNames(typeof(StringComparison)))
            { 
               StringComparison strCmp = (StringComparison) Enum.Parse(typeof(StringComparison), 
                                                      cmpName);
               string instance = strings[ctr1, 0];
               string value = strings[ctr1, 1];
               Console.WriteLine("{0} starts with {1}: {2} ({3} comparison)", 
                                 instance, value, 
                                 instance.StartsWith(value, strCmp), 
                                 strCmp); 
            }
            Console.WriteLine();   
      }   
   }
}
// The example displays the following output:
//       ABCdef starts with abc: False (CurrentCulture comparison)
//       ABCdef starts with abc: True (CurrentCultureIgnoreCase comparison)
//       ABCdef starts with abc: False (InvariantCulture comparison)
//       ABCdef starts with abc: True (InvariantCultureIgnoreCase comparison)
//       ABCdef starts with abc: False (Ordinal comparison)
//       ABCdef starts with abc: True (OrdinalIgnoreCase comparison)
//       
//       ABCdef starts with abc: False (CurrentCulture comparison)
//       ABCdef starts with abc: True (CurrentCultureIgnoreCase comparison)
//       ABCdef starts with abc: False (InvariantCulture comparison)
//       ABCdef starts with abc: True (InvariantCultureIgnoreCase comparison)
//       ABCdef starts with abc: False (Ordinal comparison)
//       ABCdef starts with abc: True (OrdinalIgnoreCase comparison)
//       
//       œil starts with oe: True (CurrentCulture comparison)
//       œil starts with oe: True (CurrentCultureIgnoreCase comparison)
//       œil starts with oe: True (InvariantCulture comparison)
//       œil starts with oe: True (InvariantCultureIgnoreCase comparison)
//       œil starts with oe: False (Ordinal comparison)
//       œil starts with oe: False (OrdinalIgnoreCase comparison)
//       
//       læring} starts with lae: True (CurrentCulture comparison)
//       læring} starts with lae: True (CurrentCultureIgnoreCase comparison)
//       læring} starts with lae: True (InvariantCulture comparison)
//       læring} starts with lae: True (InvariantCultureIgnoreCase comparison)
//       læring} starts with lae: False (Ordinal comparison)
//       læring} starts with lae: False (OrdinalIgnoreCase comparison)

open System

let strings =
    array2D 
      [ [ "ABCdef"; "abc" ]
        [ "ABCdef"; "abc" ]
        [ "œil"; "oe" ]
        [ "læring}"; "lae" ] ]

for ctr1 = strings.GetLowerBound 0 to strings.GetUpperBound 0 do
    for cmpName in Enum.GetNames typeof<StringComparison> do
        let strCmp = Enum.Parse(typeof<StringComparison>, cmpName) :?> StringComparison
        let instance = strings[ctr1, 0]
        let value = strings[ctr1, 1]
        printfn $"{instance} starts with {value}: {instance.StartsWith(value, strCmp)} ({strCmp} comparison)"
    printfn ""
// The example displays the following output:
//       ABCdef starts with abc: False (CurrentCulture comparison)
//       ABCdef starts with abc: True (CurrentCultureIgnoreCase comparison)
//       ABCdef starts with abc: False (InvariantCulture comparison)
//       ABCdef starts with abc: True (InvariantCultureIgnoreCase comparison)
//       ABCdef starts with abc: False (Ordinal comparison)
//       ABCdef starts with abc: True (OrdinalIgnoreCase comparison)
//
//       ABCdef starts with abc: False (CurrentCulture comparison)
//       ABCdef starts with abc: True (CurrentCultureIgnoreCase comparison)
//       ABCdef starts with abc: False (InvariantCulture comparison)
//       ABCdef starts with abc: True (InvariantCultureIgnoreCase comparison)
//       ABCdef starts with abc: False (Ordinal comparison)
//       ABCdef starts with abc: True (OrdinalIgnoreCase comparison)
//
//       œil starts with oe: True (CurrentCulture comparison)
//       œil starts with oe: True (CurrentCultureIgnoreCase comparison)
//       œil starts with oe: True (InvariantCulture comparison)
//       œil starts with oe: True (InvariantCultureIgnoreCase comparison)
//       œil starts with oe: False (Ordinal comparison)
//       œil starts with oe: False (OrdinalIgnoreCase comparison)
//
//       læring} starts with lae: True (CurrentCulture comparison)
//       læring} starts with lae: True (CurrentCultureIgnoreCase comparison)
//       læring} starts with lae: True (InvariantCulture comparison)
//       læring} starts with lae: True (InvariantCultureIgnoreCase comparison)
//       læring} starts with lae: False (Ordinal comparison)
//       læring} starts with lae: False (OrdinalIgnoreCase comparison)

Module Example
   Public Sub Main()
      Dim strings(,) As String = { {"ABCdef", "abc" },                    
                                   {"ABCdef", "abc" },  
                                   {"œil","oe" },
                                   { "læring}", "lae" } }
      For ctr1 As Integer = strings.GetLowerBound(0) To strings.GetUpperBound(0)
            For Each cmpName As String In [Enum].GetNames(GetType(StringComparison)) 
               Dim strCmp As StringComparison = CType([Enum].Parse(GetType(StringComparison), 
                                                      cmpName), StringComparison)
               Dim instance As String = strings(ctr1, 0)
               Dim value As String = strings(ctr1, 1)
               Console.WriteLine("{0} starts with {1}: {2} ({3} comparison)", 
                                 instance, value, 
                                 instance.StartsWith(value, strCmp), 
                                 strCmp) 
            Next
            Console.WriteLine()   
      Next   
   End Sub
End Module
' The example displays the following output:
'       ABCdef starts with abc: False (CurrentCulture comparison)
'       ABCdef starts with abc: True (CurrentCultureIgnoreCase comparison)
'       ABCdef starts with abc: False (InvariantCulture comparison)
'       ABCdef starts with abc: True (InvariantCultureIgnoreCase comparison)
'       ABCdef starts with abc: False (Ordinal comparison)
'       ABCdef starts with abc: True (OrdinalIgnoreCase comparison)
'       
'       ABCdef starts with abc: False (CurrentCulture comparison)
'       ABCdef starts with abc: True (CurrentCultureIgnoreCase comparison)
'       ABCdef starts with abc: False (InvariantCulture comparison)
'       ABCdef starts with abc: True (InvariantCultureIgnoreCase comparison)
'       ABCdef starts with abc: False (Ordinal comparison)
'       ABCdef starts with abc: True (OrdinalIgnoreCase comparison)
'       
'       œil starts with oe: True (CurrentCulture comparison)
'       œil starts with oe: True (CurrentCultureIgnoreCase comparison)
'       œil starts with oe: True (InvariantCulture comparison)
'       œil starts with oe: True (InvariantCultureIgnoreCase comparison)
'       œil starts with oe: False (Ordinal comparison)
'       œil starts with oe: False (OrdinalIgnoreCase comparison)
'       
'       læring} starts with lae: True (CurrentCulture comparison)
'       læring} starts with lae: True (CurrentCultureIgnoreCase comparison)
'       læring} starts with lae: True (InvariantCulture comparison)
'       læring} starts with lae: True (InvariantCultureIgnoreCase comparison)
'       læring} starts with lae: False (Ordinal comparison)
'       læring} starts with lae: False (OrdinalIgnoreCase comparison)

Commenti

Il StartsWith metodo confronta il value parametro con la sottostringa all'inizio di questa stringa e restituisce un valore che indica se sono uguali. Per essere uguale, value deve essere un riferimento a questa stessa stringa, deve essere la stringa vuota ("") o deve corrispondere all'inizio di questa stringa. Il tipo di confronto eseguito dal StartsWith metodo dipende dal valore del comparisonType parametro . Il confronto può usare le convenzioni delle impostazioni cultura correnti (StringComparison.CurrentCulture e StringComparison.CurrentCultureIgnoreCase) o delle impostazioni cultura invarianti (StringComparison.InvariantCulture e StringComparison.InvariantCultureIgnoreCase) oppure può essere costituito da un confronto carattere per carattere di punti di codice (StringComparison.Ordinal o StringComparison.OrdinalIgnoreCase). Il confronto può anche fare distinzione tra maiuscole e minuscole (StringComparison.CurrentCulture, StringComparison.InvariantCultureo StringComparison.Ordinal) oppure può ignorare la distinzione tra maiuscole e minuscole (StringComparison.CurrentCultureIgnoreCase, StringComparison.InvariantCultureIgnoreCase, StringComparison.OrdinalIgnoreCase).

Vedi anche

Si applica a

StartsWith(Char)

Origine:
String.Comparison.cs
Origine:
String.Comparison.cs
Origine:
String.Comparison.cs

Determina se questa istanza di stringa inizia con il carattere specificato.

public:
 bool StartsWith(char value);
public bool StartsWith (char value);
member this.StartsWith : char -> bool
Public Function StartsWith (value As Char) As Boolean

Parametri

value
Char

Carattere da confrontare.

Restituisce

Boolean

true se l'inizio di questa stringa corrisponde al parametro value; in caso contrario, false.

Commenti

Questo metodo esegue un confronto ordinale (con distinzione tra maiuscole e minuscole e senza distinzione tra impostazioni cultura).

Si applica a

StartsWith(String)

Origine:
String.Comparison.cs
Origine:
String.Comparison.cs
Origine:
String.Comparison.cs

Determina se l'inizio di questa istanza di stringa corrisponde alla stringa specificata.

public:
 bool StartsWith(System::String ^ value);
public bool StartsWith (string value);
member this.StartsWith : string -> bool
Public Function StartsWith (value As String) As Boolean

Parametri

value
String

Stringa da confrontare.

Restituisce

Boolean

true se l'inizio di questa stringa corrisponde al parametro value; in caso contrario, false.

Eccezioni

ArgumentNullException

value è null.

Esempio

Nell'esempio seguente viene definito un StripStartTags metodo che usa il StartsWith(String) metodo per rimuovere i tag di inizio HTML dall'inizio di una stringa. Si noti che il StripStartTags metodo viene chiamato in modo ricorsivo per assicurarsi che all'inizio della riga vengano rimossi più tag di inizio HTML. L'esempio non rimuove i tag HTML incorporati in una stringa.

using namespace System;

String^ StripStartTags( String^ item )
{
   // Determine whether a tag begins the string.
   if (item->Trim()->StartsWith("<")) {
      // Find the closing tag.
      int lastLocation = item->IndexOf(">");
      
      // Remove the tag.
      if ( lastLocation >= 0 ) {
         item = item->Substring(lastLocation+ 1);
            
         // Remove any additional starting tags.
         item = StripStartTags(item);
      }      
   }

   return item;
}

int main()
{
   array<String^>^ strSource = { "<b>This is bold text</b>",
                   "<H1>This is large Text</H1>",
                   "<b><i><font color=green>This has multiple tags</font></i></b>",
                   "<b>This has <i>embedded</i> tags.</b>",
                   "<This line simply begins with a lesser than symbol, it should not be modified" };
   
   // Display the initial string array.
   Console::WriteLine("The original strings:");
   Console::WriteLine("---------------------");
   for each (String^ s in strSource)    
      Console::WriteLine( s );
   Console::WriteLine();

   Console::WriteLine( "Strings after starting tags have been stripped:");
   Console::WriteLine( "-----------------------------------------------");
   
   // Display the strings with starting tags removed.
   for each (String^ s in strSource)
      Console::WriteLine(StripStartTags(s));
}
// The example displays the following output:
//    The original strings:
//    ---------------------
//    <b>This is bold text</b>
//    <H1>This is large Text</H1>
//    <b><i><font color = green>This has multiple tags</font></i></b>
//    <b>This has <i>embedded</i> tags.</b>
//    <This line simply begins with a lesser than symbol, it should not be modified
//    
//    Strings after starting tags have been stripped:
//    -----------------------------------------------
//    This is bold text</b>
//    This is large Text</H1>
//    This has multiple tags</font></i></b>
//    This has <i>embedded</i> tags.</b>
//    <This line simply begins with a lesser than symbol, it should not be modified

using System;

public class Example
{
   public static void Main() {
      string [] strSource = { "<b>This is bold text</b>", "<H1>This is large Text</H1>",
                "<b><i><font color=green>This has multiple tags</font></i></b>",
                "<b>This has <i>embedded</i> tags.</b>",
                "<This line simply begins with a lesser than symbol, it should not be modified" };

      // Display the initial string array.
      Console.WriteLine("The original strings:");
      Console.WriteLine("---------------------");
      foreach (var s in strSource)
         Console.WriteLine(s);
      Console.WriteLine();

      Console.WriteLine("Strings after starting tags have been stripped:");
      Console.WriteLine("-----------------------------------------------");

      // Display the strings with starting tags removed.
     foreach (var s in strSource)
        Console.WriteLine(StripStartTags(s));
   }

   private static string StripStartTags(string item)
   {
      // Determine whether a tag begins the string.
      if (item.Trim().StartsWith("<")) {
         // Find the closing tag.
         int lastLocation = item.IndexOf( ">" );
         // Remove the tag.
         if (lastLocation >= 0) {
            item =  item.Substring( lastLocation + 1 );

            // Remove any additional starting tags.
            item = StripStartTags(item);
         }
      }

      return item;
   }
}
// The example displays the following output:
//    The original strings:
//    ---------------------
//    <b>This is bold text</b>
//    <H1>This is large Text</H1>
//    <b><i><font color = green>This has multiple tags</font></i></b>
//    <b>This has <i>embedded</i> tags.</b>
//    <This line simply begins with a lesser than symbol, it should not be modified
//
//    Strings after starting tags have been stripped:
//    -----------------------------------------------
//    This is bold text</b>
//    This is large Text</H1>
//    This has multiple tags</font></i></b>
//    This has <i>embedded</i> tags.</b>
//    <This line simply begins with a lesser than symbol, it should not be modified

let rec stripStartTags (item: string) =
    // Determine whether a tag begins the string.
    if item.Trim().StartsWith "<" then
        // Find the closing tag.
        let lastLocation = item.IndexOf ">"
        // Remove the tag.
        let item = 
            if lastLocation >= 0 then
                item.Substring( lastLocation + 1 )
            else 
                item

        // Remove any additional starting tags.
        stripStartTags item
    else
        item

let strSource = 
    [| "<b>This is bold text</b>"; "<H1>This is large Text</H1>"
       "<b><i><font color=green>This has multiple tags</font></i></b>"
       "<b>This has <i>embedded</i> tags.</b>"
       "<This line simply begins with a lesser than symbol, it should not be modified" |]

// Display the initial string array.
printfn "The original strings:"
printfn "---------------------"
for s in strSource do
    printfn $"{s}"
printfn ""

printfn "Strings after starting tags have been stripped:"
printfn "-----------------------------------------------"

// Display the strings with starting tags removed.
for s in strSource do
    printfn $"{stripStartTags s}"

// The example displays the following output:
//    The original strings:
//    ---------------------
//    <b>This is bold text</b>
//    <H1>This is large Text</H1>
//    <b><i><font color = green>This has multiple tags</font></i></b>
//    <b>This has <i>embedded</i> tags.</b>
//    <This line simply begins with a lesser than symbol, it should not be modified
//
//    Strings after starting tags have been stripped:
//    -----------------------------------------------
//    This is bold text</b>
//    This is large Text</H1>
//    This has multiple tags</font></i></b>
//    This has <i>embedded</i> tags.</b>
//    <This line simply begins with a lesser than symbol, it should not be modified

Public Class Example
   Public Shared Sub Main()
      Dim strSource() As String = { "<b>This is bold text</b>", 
                         "<H1>This is large Text</H1>", 
                         "<b><i><font color = green>This has multiple tags</font></i></b>", 
                         "<b>This has <i>embedded</i> tags.</b>", 
                         "<This line simply begins with a lesser than symbol, it should not be modified" }

      ' Display the initial string array.
      Console.WriteLine("The original strings:")
      Console.WriteLine("---------------------")
      For Each s In strSource
         Console.WriteLine(s)
      Next 
      Console.WriteLine()

      Console.WriteLine("Strings after starting tags have been stripped:")
      Console.WriteLine("-----------------------------------------------") 

      ' Display the strings with starting tags removed.
      For Each s In strSource
         Console.WriteLine(StripStartTags(s))
      Next 
   End Sub 

   Private Shared Function StripStartTags(item As String) As String
      ' Determine whether a tag begins the string.
      If item.Trim().StartsWith("<") Then
         ' Find the closing tag.
         Dim lastLocation As Integer = item.IndexOf(">")
         If lastLocation >= 0 Then
            ' Remove the tag.
            item = item.Substring((lastLocation + 1))
            
            ' Remove any additional starting tags.
            item = StripStartTags(item)
         End If
      End If
      
      Return item
   End Function 
End Class 
' The example displays the following output:
'    The original strings:
'    ---------------------
'    <b>This is bold text</b>
'    <H1>This is large Text</H1>
'    <b><i><font color = green>This has multiple tags</font></i></b>
'    <b>This has <i>embedded</i> tags.</b>
'    <This line simply begins with a lesser than symbol, it should not be modified
'    
'    Strings after starting tags have been stripped:
'    -----------------------------------------------
'    This is bold text</b>
'    This is large Text</H1>
'    This has multiple tags</font></i></b>
'    This has <i>embedded</i> tags.</b>
'    <This line simply begins with a lesser than symbol, it should not be modified

Commenti

Questo metodo confronta value la sottostringa all'inizio di questa istanza con la stessa lunghezza valuedi e restituisce un'indicazione se sono uguali. Per essere uguale, value deve essere una stringa vuota (String.Empty), deve essere un riferimento a questa stessa istanza oppure deve corrispondere all'inizio di questa istanza.

Questo metodo esegue un confronto di parole (con distinzione tra maiuscole e minuscole e con distinzione tra impostazioni cultura) usando le impostazioni cultura correnti.

Note per i chiamanti

Come illustrato in Procedure consigliate per l'uso di stringhe, è consigliabile evitare di chiamare metodi di confronto tra stringhe che sostituiscono i valori predefiniti e chiamare invece metodi che richiedono parametri da specificare in modo esplicito. Per determinare se una stringa inizia con una determinata sottostringa usando le regole di confronto tra stringhe delle impostazioni cultura correnti, segnalare in modo esplicito l'intenzione chiamando l'overload del StartsWith(String, StringComparison) metodo con un valore di CurrentCulture per il comparisonType relativo parametro. Se non è necessario un confronto con riconoscimento linguistico, è consigliabile usare Ordinal.

Vedi anche

Si applica a