Updated: September 2011
Retrieves a reference to a specified String.
Assembly: mscorlib (in mscorlib.dll)
Public Shared Function IsInterned ( _
str As String _
) As Stringpublic static string IsInterned(
string str
)public:
static String^ IsInterned(
String^ str
)static member IsInterned :
str:string -> string
Parameters
- str
- Type: System
. . :: . String
The string to search for in the intern pool.
Return Value
Type: SystemA reference to str if it is in the common language runtime intern pool; otherwise,
| Exception | Condition |
|---|---|
| ArgumentNullException | str is |
The common language runtime automatically maintains a table, called the intern pool, which contains a single instance of each unique literal string constant declared in a program, as well as any unique instance of String you add programmatically.
The intern pool conserves string storage. If you assign a literal string constant to several variables, each variable is set to reference the same constant in the intern pool instead of referencing several different instances of String that have identical values.
This method looks up str in the intern pool. If str has already been interned, a reference to that instance is returned; otherwise,
Compare this method to the Intern method.
This method does not return a Boolean value. If you call the method because you want a Boolean value that indicates whether a particular string is interned, you can use code such as the following.
Module Example
Public Sub Main()
Dim str1 As String = "a"
Dim str2 As String = str1 + "b"
Dim str3 As String = str2 + "c"
Dim strings() As String = { "value", "part1" + "_" + "part2", str3,
String.Empty, Nothing }
For Each value In strings
If value Is Nothing Then Continue For
Dim interned As Boolean = (String.IsInterned(value) IsNot Nothing)
If interned Then
Console.WriteLine("'{0}' is in the string intern pool.",
value)
Else
Console.WriteLine("'{0}' is not in the string intern pool.",
value)
End If
Next
End Sub
End Module
' The example displays the following output:
' 'value' is in the string intern pool.
' 'part1_part2' is in the string intern pool.
' 'abc' is not in the string intern pool.
' '' is in the string intern pool.
using System;
public class Example
{
public static void Main()
{
string str1 = "a";
string str2 = str1 + "b";
string str3 = str2 + "c";
string[] strings = { "value", "part1" + "_" + "part2", str3,
String.Empty, null };
foreach (var value in strings) {
if (value == null) continue;
bool interned = String.IsInterned(value) != null;
if (interned)
Console.WriteLine("'{0}' is in the string intern pool.",
value);
else
Console.WriteLine("'{0}' is not in the string intern pool.",
value);
}
}
}
// The example displays the following output:
// 'value' is in the string intern pool.
// 'part1_part2' is in the string intern pool.
// 'abc' is not in the string intern pool.
// '' is in the string intern pool.
.gif) Note |
|---|
Starting with the .NET Framework 2.0, you can override the use of the intern pool when you use the Ngen.exe (Native Image Generator) to install an assembly to the native image cache on a local computer. For more information, see Performance Considerations in the Remarks section for the Intern property. |
The following example demonstrates that literal strings are interned automatically by the compiler.
' Sample for String.IsInterned(String)
Imports System
Imports System.Text
Imports System.Runtime.CompilerServices
' In the .NET Framework 2.0 the following attribute declaration allows you to
' avoid the use of the interning when you use NGEN.exe to compile an assembly
' to the native image cache.
<Assembly: CompilationRelaxations(CompilationRelaxations.NoStringInterning)>
Class Sample
Public Shared Sub Main()
' String str1 is known at compile time, and is automatically interned.
Dim str1 As [String] = "abcd"
' Constructed string, str2, is not explicitly or automatically interned.
Dim str2 As [String] = New StringBuilder().Append("wx").Append("yz").ToString()
Console.WriteLine()
Test(1, str1)
Test(2, str2)
End Sub 'Main
Public Shared Sub Test(ByVal sequence As Integer, ByVal str As [String])
Console.Write("{0}) The string, '", sequence)
Dim strInterned As [String] = [String].IsInterned(str)
If strInterned Is Nothing Then
Console.WriteLine("{0}', is not interned.", str)
Else
Console.WriteLine("{0}', is interned.", strInterned)
End If
End Sub 'Test
End Class 'Sample '
'This example produces the following results:
'1) The string, 'abcd', is interned.
'2) The string, 'wxyz', is not interned.
'If you use NGEN.exe to compile the assembly to the native image cache, this
'example produces the following results:
'1) The string, 'abcd', is not interned.
'2) The string, 'wxyz', is not interned.
// Sample for String.IsInterned(String)
using System;
using System.Text;
using System.Runtime.CompilerServices;
// In the .NET Framework 2.0 the following attribute declaration allows you to
// avoid the use of the interning when you use NGEN.exe to compile an assembly
// to the native image cache.
[assembly: CompilationRelaxations(CompilationRelaxations.NoStringInterning)]
class Sample
{
public static void Main()
{
// String str1 is known at compile time, and is automatically interned.
String str1 = "abcd";
// Constructed string, str2, is not explicitly or automatically interned.
String str2 = new StringBuilder().Append("wx").Append("yz").ToString();
Console.WriteLine();
Test(1, str1);
Test(2, str2);
}
public static void Test(int sequence, String str)
{
Console.Write("{0}) The string, '", sequence);
String strInterned = String.IsInterned(str);
if (strInterned == null)
Console.WriteLine("{0}', is not interned.", str);
else
Console.WriteLine("{0}', is interned.", strInterned);
}
}
//This example produces the following results:
//1) The string, 'abcd', is interned.
//2) The string, 'wxyz', is not interned.
//If you use NGEN.exe to compile the assembly to the native image cache, this
//example produces the following results:
//1) The string, 'abcd', is not interned.
//2) The string, 'wxyz', is not interned.
// Sample for String::IsInterned(String)
using namespace System;
using namespace System::Text;
using namespace System::Runtime::CompilerServices;
// In the .NET Framework 2.0 the following attribute declaration allows you to
// avoid the use of the interning when you use NGEN.exe to compile an assembly
// to the native image cache.
[assembly:CompilationRelaxations(CompilationRelaxations::NoStringInterning)];
void Test( int sequence, String^ str )
{
Console::Write( "{0} The string '", sequence );
String^ strInterned = String::IsInterned( str );
if ( strInterned == nullptr )
Console::WriteLine( "{0}' is not interned.", str );
else
Console::WriteLine( "{0}' is interned.", strInterned );
}
int main()
{
// String str1 is known at compile time, and is automatically interned.
String^ str1 = "abcd";
// Constructed string, str2, is not explicitly or automatically interned.
String^ str2 = (gcnew StringBuilder)->Append( "wx" )->Append( "yz" )->ToString();
Console::WriteLine();
Test( 1, str1 );
Test( 2, str2 );
}
//This example produces the following results:
//1) The string, 'abcd', is interned.
//2) The string, 'wxyz', is not interned.
//If you use NGEN.exe to compile the assembly to the native image cache, this
//example produces the following results:
//1) The string, 'abcd', is not interned.
//2) The string, 'wxyz', is not interned.
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.