Queue::Peek Method
Returns the object at the beginning of the Queue without removing it.
Namespace: System.Collections
Assembly: mscorlib (in mscorlib.dll)
| Exception | Condition |
|---|---|
| InvalidOperationException | The Queue is empty. |
This method is similar to the Dequeue method, but Peek does not modify the Queue.
nullptr 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 */
Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)
The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.
