PRB: Assertion Failed - SOCKCORE.CPP, Line 51

The information in this article applies to:

• The Microsoft Foundation Classes (MFC) included with: Microsoft Visual C++ for Windows, version 1.52

SYMPTOMS

An application using MFC's socket classes (CSocket and CAsyncSocket) causes an assertion failure upon exit. The assertion failure text is similar to this:

   myapp Windows Application: File sockcore.cpp, Line 51, Assertion Failed!

CAUSE

This assertion failure most likely occurs if any CSocket or CAsyncSocket objects have not been closed (or destroyed).

RESOLUTION

Ensure that all socket objects in the application are properly closed and destroyed. If a socket object has been used but was not destroyed, this message will occur.

Here is a technique you can use to determine which socket object was not destroyed:

1. Make sure that tracing has been enabled by running the "MFC Trace Options" program, which can be found in the Visual C++ group. Select the Enable Tracing check box.

2. Debug the application using the Visual Workbench Debugger:

   Select Debug.Go

3. When the Assertion Failed! message box appears for this assertion, select Ignore.

   Detected memory leaks!
   Dumping objects ->
   {2} a CSocket at $DEF0932 m_hSocket = 0x2
   m_pbBlocking = $0
   m_nConnectError = -1
   Object dump complete.

STATUS

This behavior is by design.

MORE INFORMATION

For more information on how to track down memory leaks, please see the following article in the Microsoft Knowledge Base:

   ARTICLE-ID: Q122307
   TITLE     : Tracking Down Memory Leaks with _afxBreakAlloc

Sockets require a window to receive notification messages when socket events occur (when data is ready to be received on the socket). MFC manages this notification window for you when you use the MFC socket classes.

This window is created by MFC when your application uses a socket object. When all of the socket objects have been closed, MFC destroys the notification window.

The assertion failure message is generated by the following line:

   ASSERT(_afxSockState->hSocketWindow == NULL);

A common scenario where this might occur is with a server application that opens a listening socket, and the listening socket is left open throughout the execution of the application. In this scenario, you may easily overlook the need to destroy the socket object. For example:

   BOOL CMyApp::InitInstance()
   {
      // ...
      m_pSock = new CListeningSocket;
      m_pSock->Create(nPort);
      m_pSock->Listen();
      // ...
      return CWinApp::InitInstance();
   }

   int CMyApp::ExitInstance()
   {
      delete m_pSock;
      return CWinapp::ExitInstance();
   }