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Posted 20 Oct 2002

Useful macros for pointer verification

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A few macros to validate pointers passed to functions.
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Most know the useful macros provided by various libraries named ASSERT, VERIFY (and similar) which just validates the provided argument. If the validation evaluates to false then a debug notification is raised.

In many cases this is sufficient for simple verifications but validating pointers is not the strength of this methods. Look at this example:

void MyFunction(LPSOMESTRUCT pData)
  ASSERT(pData != NULL);
  // ... more code
When you pass a NULL pointer to this function it will correctly detect it, but what if you pass 0xcdcdcdcd ? Its not NULL and its most probably not a valid address either. ASSERT will not catch it and you application will throw an exception.

More Macros

Here is a more advanced solution required. One possible solution is the use of the functions provided by the Windows API: IsBadReadPtr(), IsBadWritePtr(), IsBadStringPtr(). These functions take a memory location and a size as arguments and verify that the calling process really has read and/or write access to the location. It might be that the memory at the location is only partially accessible from your process, or that the memory is read or write only. These functions also detect this situations.

I've wrapped this functions into handy macros which you can use similar to the ASSERT and VERIFY macros.

#ifdef _DEBUG

       { if(::IsBadWritePtr(a, sizeof(LPDWORD))) \
		{ ::OutputDebugString(_T("Parameter ") _T(#a) \
		_T(" is not a valid write pointer\r\n"));}}
		{ if(::IsBadReadPtr(a, sizeof(LPDWORD)))\
		{ ::OutputDebugString(_T("Parameter ") _T(#a) \
		_T(" is not a valid read pointer\r\n"));}}

		{ if(::IsBadWritePtr(a, l)) \
		{ ::OutputDebugString(_T("Parameter ") _T(#a) \
		_T(" is not a valid write area\r\n"));}}
#define VERIFY_ISREADDATA(a, l)\
		{ if(::IsBadReadPtr(a, l))  \
		{ ::OutputDebugString(_T("Parameter ") _T(#a) \
		_T(" is not a valid read area\r\n"));}}

		{ if(::IsBadWritePtr(a, sizeof(LPDWORD))) \
		{ ::OutputDebugString(_T("Parameter ") _T(#a) \
		_T(" is not a valid write pointer\r\n")); ASSERT(false);}}
		{ if(::IsBadReadPtr(a, sizeof(LPDWORD)))  \
		{ ::OutputDebugString(_T("Parameter ") _T(#a) \
		_T(" is not a valid read pointer\r\n")); ASSERT(false);}}

		{ if(::IsBadWritePtr(a, l)) \
		{ ::OutputDebugString(_T("Parameter ") _T(#a) \
		_T(" is not a valid write area\r\n")); ASSERT(false);}}
#define ASSERT_ISREADDATA(a, l)		{ if(::IsBadReadPtr(a, l))  \
		{ ::OutputDebugString(_T("Parameter ") _T(#a)\
		_T(" is not a valid read area\r\n")); ASSERT(false);}}



#define VERIFY_ISREADDATA(a, l)	




Our sample from before can be changed to this:

void MyFunction(LPSOMESTRUCT pData)
  // ... more code
Now it will correctly assert when you pass the address 0xcdcdcdcd or any other location from which the function can not read at least sizeof(SOMESTRUCT) bytes and the debug output will show "Parameter pData is not a valid read area".

I have found this to be a valuable tool when you write functions which take in or out pointers. Many problems related to bad pointers can easily be cured by using these validation macros.


This is compatible with any Windows version without restriction. It can be used with any Visual C++ version and all eVC versions. Anyway, using the macros is your responsability :)


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Comments and Discussions

GeneralGuaranteed Multithreading Problems Pin
pg--az12-Jun-09 3:22
memberpg--az12-Jun-09 3:22 
GeneralThese IsBadxxx functions are dangerous! Pin
AaronJRidout31-Oct-07 6:38
memberAaronJRidout31-Oct-07 6:38 
GeneralRe: These IsBadxxx functions are dangerous! Pin
Andreas Saurwein Franci Gonalves31-Oct-07 6:56
memberAndreas Saurwein Franci Gonalves31-Oct-07 6:56 
As you may notice, these functions are obsolete by now. The article was written in 2002 when Windows 95 was still widely used and application security was just a faint thought of some weirdos.

Leon[^] - Enterprise Anti-Spam Server

GeneralRe: These IsBadxxx functions are dangerous! Pin
Blake Miller2-May-08 6:29
memberBlake Miller2-May-08 6:29 
Generalevc support Pin
hillol sarker12-Oct-04 23:17
memberhillol sarker12-Oct-04 23:17 
GeneralRe: evc support Pin
Liby Baby6-Jul-05 19:17
sussLiby Baby6-Jul-05 19:17 
Generalnew -> delete -> valid pointer Pin
Thomas Knauth18-Nov-02 6:14
memberThomas Knauth18-Nov-02 6:14 
GeneralRe: new -> delete -> valid pointer Pin
Andreas Saurwein18-Nov-02 6:45
memberAndreas Saurwein18-Nov-02 6:45 
GeneralRe: new -> delete -> valid pointer Pin
Philippe Lhoste2-Dec-02 5:56
memberPhilippe Lhoste2-Dec-02 5:56 
GeneralRe: new -> delete -> valid pointer Pin
Andreas Saurwein2-Dec-02 13:04
memberAndreas Saurwein2-Dec-02 13:04 

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