Queue::Peek Method ()

 

Returns the object at the beginning of the Queue without removing it.

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

public:
virtual Object^ Peek()

Return Value

Type: System::Object^

The object at the beginning of the Queue.

Exception Condition
InvalidOperationException

The Queue is empty.

This method is similar to the Dequeue method, but Peek does not modify the Queue.

null can be added to the Queue as a value. To distinguish between a null value and the end of the Queue, check the Count property or catch the InvalidOperationException, which is thrown when the Queue is empty.

This method is an O(1) operation.

The following example shows how to add elements to the Queue, remove elements from the Queue, or view the element at the beginning of the Queue.

using namespace System;
using namespace System::Collections;
void PrintValues( IEnumerable^ myCollection );
int main()
{

   // Creates and initializes a new Queue.
   Queue^ myQ = gcnew Queue;
   myQ->Enqueue( "The" );
   myQ->Enqueue( "quick" );
   myQ->Enqueue( "brown" );
   myQ->Enqueue( "fox" );

   // Displays the Queue.
   Console::Write( "Queue values:" );
   PrintValues( myQ );

   // Removes an element from the Queue.
   Console::WriteLine( "(Dequeue)\t{0}", myQ->Dequeue() );

   // Displays the Queue.
   Console::Write( "Queue values:" );
   PrintValues( myQ );

   // Removes another element from the Queue.
   Console::WriteLine( "(Dequeue)\t{0}", myQ->Dequeue() );

   // Displays the Queue.
   Console::Write( "Queue values:" );
   PrintValues( myQ );

   // Views the first element in the Queue but does not remove it.
   Console::WriteLine( "(Peek)   \t{0}", myQ->Peek() );

   // Displays the Queue.
   Console::Write( "Queue values:" );
   PrintValues( myQ );
}

void PrintValues( IEnumerable^ myCollection )
{
   IEnumerator^ myEnum = myCollection->GetEnumerator();
   while ( myEnum->MoveNext() )
   {
      Object^ obj = safe_cast<Object^>(myEnum->Current);
      Console::Write( "    {0}", obj );
   }

   Console::WriteLine();
}

/* 
 This code produces the following output.

 Queue values:    The    quick    brown    fox
 (Dequeue)       The
 Queue values:    quick    brown    fox
 (Dequeue)       quick
 Queue values:    brown    fox
 (Peek)          brown
 Queue values:    brown    fox

 */

Universal Windows Platform
Available since 10
.NET Framework
Available since 1.1
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