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Useful macros for pointer verification

By , 20 Oct 2002
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Introduction

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

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

#define VERIFY_ISWRITEDATA(a, l)\
		{ 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"));}}

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

#define ASSERT_ISWRITEDATA(a, l)\
		{ 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);}}

#else

#define VERIFY_ISWRITEPOINTER(a)
#define VERIFY_ISREADPOINTER(a)	

#define VERIFY_ISWRITEDATA(a, l)
#define VERIFY_ISREADDATA(a, l)	

#define ASSERT_ISWRITEPOINTER(a)
#define ASSERT_ISREADPOINTER(a)

#define ASSERT_ISWRITEDATA(a, l)
#define ASSERT_ISREADDATA(a, l)

#endif

Our sample from before can be changed to this:

void MyFunction(LPSOMESTRUCT pData)
{
  ASSERT_ISREADDATA(pData, sizeof(SOMESTRUCT));
  // ... 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.

Compatibility

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 Smile | :)

License

This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

A list of licenses authors might use can be found here

About the Author

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Comments and Discussions

 
GeneralRe: Remove MFC dependency... PinmemberNguyen Binh22-Oct-02 1:37 
GeneralRe: Remove MFC dependency... PinmemberAndreas Saurwein22-Oct-02 3:00 
GeneralRe: Remove MFC dependency... PinmemberNguyen Binh23-Oct-02 0:02 
GeneralRe: Remove MFC dependency... PinmemberAndreas Saurwein23-Oct-02 0:52 
GeneralRe: Remove MFC dependency... PinmemberArmen Hakobyan21-Oct-02 22:54 
GeneralRe: Remove MFC dependency... Pinmember.:fl0yd:.14-Jun-03 13:33 
General0.4 kb PinsussAnonymous21-Oct-02 15:32 
GeneralRe: 0.4 kb PinmemberAndreas Saurwein21-Oct-02 22:56 
Initially I was even thinking of omiting the download Smile | :)
Then I thought of all the newbies that still dont know how to copy a selection from a webpage and added the huge zip file. Cool | :cool:
 
I keep submitting “VB” as a Priority-1 bug, but apparently no one here knows how to fix it. Nick Hodapp, Semicolon

GeneralRe: 0.4 kb PinmemberNorm Almond22-Oct-02 0:06 
Generalverify vs trace PinmemberHugo Hallman21-Oct-02 5:55 
GeneralRe: verify vs trace PinmemberAndreas Saurwein21-Oct-02 6:10 
GeneralHelpfull PinmemberRoger Allen21-Oct-02 5:48 
GeneralTwo in one :) PinmemberArmen Hakobyan21-Oct-02 5:37 
GeneralRe: Two in one :) PinmemberAndreas Saurwein21-Oct-02 6:12 
GeneralRe: Two in one :) PinmemberRoger Allen23-Oct-02 2:38 
GeneralFormatting PinmemberGiles21-Oct-02 5:29 
GeneralRe: Formatting PinmemberAndreas Saurwein21-Oct-02 6:15 
GeneralRe: Formatting PinmemberGiles21-Oct-02 8:05 

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