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Home » Tip Bank » C++
Language: C++
Expertise: Advanced
Feb 13, 2002

Check the Validity of the Memory Allocated to a Calling Process


Some of the most irritating and difficult-to-trace bugs are the ones relating to uninitialized or inaccessible memory locations. This problem becomes especially severe when dealing with parameters that are pointers. If the pointers happen to be NULL or dangling, they might lead to data corruption and ultimate demise of the application. This is especially true in case of COM applications where the conversion from an in-proc to out-proc suddenly leads to inaccessible memory locations. For this purpose we have a set of Memory Management calls such as IsBadReadPtr, IsBadWritePtr, IsBadStringPtr, and IsBadCodePtr. These methods can be used to detect if the calling process has read/write permissions over the specified memory locations pointed to by the respective pointers. It is quite advisable to check for the in parameters with IsBadReadPtr and the out parameters with IsBadWritePtr before proceeding with the business end of the function or method. A sample code set would look like this:
 
STDMETHODIMP CMyClass::MyFunc(/*in*/ int nParam1, /*out*/_
 BSTR
*pbstrParam2)
{
	BOOL bCheck = IsBadReadPtr(nParam1, sizeof(int));
	if (bCheck == 0)
	{
	bCheck = IsBadWritePtr(pbstrParam2, sizeof(BSTR));
}

if (bCheck !=0)
{
	return E_FAIL;
}

	/*Business Code Goes here*/

	return S_OK;
}
C.V. Ram
 
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