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ihttpcachekey-getisprefix-method.md

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title IHttpCacheKey::GetIsPrefix Method
description Learn how the IHttpCacheKey::GetIsPrefix method returns a value that indicates whether two IHttpCacheKey pointers have the same prefix.
ms.date 10/07/2016
ms.assetid 12816d70-6ae9-8035-f7d1-e4ceb2b78db0

IHttpCacheKey::GetIsPrefix Method

Returns a value that indicates whether two IHttpCacheKey pointers have the same prefix.

Syntax

virtual bool GetIsPrefix(  
   IHttpCacheKey* pCacheCompareKey  
) const = 0;

Parameters

pCacheCompareKey
A pointer to an IHttpCacheKey to compare with the current IHttpCacheKey.

Return Value

true if the current IHttpCacheKey has the same prefix as the pCacheCompareKey parameter; otherwise, false.

Remarks

CGlobalModule derived classes that register for GL_CACHE_OPERATION events receive an ICacheProvider pointer as a parameter on the CGlobalModule::OnGlobalCacheOperationvirtual method. You can retrieve an IHttpCacheKey pointer by calling the ICacheProvider::GetCacheKey method on the ICacheProvider pointer. You can then comparing two IHttpCacheKey pointers by calling the GetIsPrefix method.

The pCacheCompareKey parameter must not be NULL; otherwise, GetIsPrefix will throw an access violation. In addition, pCacheCompareKey must be the same extended interface type as the current IHttpCacheKey pointer. For example, if the current IHttpCacheKey pointer implements the IFileKey interface, the pCacheCompareKey parameter must implement IFileKey, as well.

The GetIsPrefix return value depends on both interface and implementation. You should use the following information as a guideline, but it may not be correct in all scenarios:

  • Classes that implement IFileKey return true only if the IFileKey::GetPath method on the current IHttpCacheKey pointer returns a PCWSTR that is a substring of the PCWSTR returned from the same method on the pCacheCompareKey pointer, starting at index 0.

  • Classes that implement the IHttpTokenKey interface return false.

  • Classes that implement the IUriKey interface return false immediately if the IUriKey::GetSiteId value of the current IHttpCacheKey pointer is not the same as the value returned from the same method on the pCacheCompareKey parameter. Otherwise, GetIsPrefix returns true only if the IUriKey::GetUrl method on the current IHttpCacheKey pointer returns a PCWSTR that is a substring of the PCWSTR returned from the same method on the pCacheCompareKey pointer, starting at index 0.

Example

The following code example demonstrates how to create a global module that listens for GL_CACHE_OPERATION and GL_CACHE_CLEANUP events and then writes the IHttpCacheKey and the GetIsPrefix information to the Event Viewer. It also demonstrates that if the same IHttpCacheKey pointer is compared against itself, the GetIsPrefix method will return true.

Caution

[!INCLUDEiisver] generates a large number of events in the Event Viewer. To avoid a log overflow error in a production environment, you should generally avoid writing cache information to the event log. For demonstration purposes, this code example writes an entry to the Event Viewer in debug mode only.

[!code-cppIHttpCacheKey#5]

The above code writes new events to the Event Viewer, where the Data box contains strings similar to the following. If the cache name is TOKEN, false is returned.

IHttpCacheKey::GetIsPrefix: true  

IHttpCacheKey::GetIsPrefix: false

Your module must export the RegisterModule function. You can export this function by creating a module definition (.def) file for your project, or you can compile the module by using the /EXPORT:RegisterModule switch. For more information, see Walkthrough: Creating a Request-Level HTTP Module By Using Native Code.

You can optionally compile the code by using the __stdcall (/Gz) calling convention instead of explicitly declaring the calling convention for each function.

Requirements

Type Description
Client - IIS 7.0 on [!INCLUDEwinvista]
- IIS 7.5 on Windows 7
- IIS 8.0 on Windows 8
- IIS 10.0 on Windows 10
Server - IIS 7.0 on [!INCLUDEwinsrv2008]
- IIS 7.5 on Windows Server 2008 R2
- IIS 8.0 on Windows Server 2012
- IIS 8.5 on Windows Server 2012 R2
- IIS 10.0 on Windows Server 2016
Product - IIS 7.0, IIS 7.5, IIS 8.0, IIS 8.5, IIS 10.0
- [!INCLUDEiisexp75], [!INCLUDEiisexp80], [!INCLUDEiisexp100]
Header Httpserv.h

See Also

IHttpCacheKey Interface