Overlapping multidimensional array corruption [closed] - c++

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I have a very insidious issue with two dynamically allocated and reallocated multidimensional arrays, defined as follows:
int *pRawVals[20][181];
and
int *pMaxPlaneRawPlanes[20][46];
These are allocated in a single function: (code condensed for clarity)
...
// iNlat and iNVer bounds checked and OK
for (int lat = 0; lat < iNlat; lat++)
{
pData->pBlendedRawPlanes[lat] = new long long[1 * (iNver + 1)];
for (int sensor = 0; sensor < 20; sensor++)
{
pData->pRawVals[sensor][lat] = new int[1 * (iNver + 1)];
for (int vert = 0; vert <= iNver; vert++)
{
pData->pRawVals[sensor][lat][vert] = SENSOR_UNREAD;
} // end for
} // end for
} // end for
...
for (int sensor = 0; sensor < 20; sensor++)
{
delete[] pData->strayVals[sensor];
pData->strayVals[sensor] = new int[1 * (iNver + 1)];
for (int vert = 0; vert < iNver + 1; vert++)
{
pData->strayVals[sensor][vert] = SENSOR_UNREAD;
} // end for
for (int lat = 0; lat < 46; lat++)
{
pData->pMaxPlaneRawPlanes[sensor][lat] = new int[361];
// for (int iFillMem = 0; iFillMem < 361; iFillMem++)
for (int vert = 0; vert < iNver; vert++)
{
pData->pMaxPlaneRawPlanes[sensor][lat][vert] = SENSOR_UNREAD;
} // end for
} // end for
} // end for
... and deallocated in another function:
for (int lat = 0; lat < pData->iNUserLats; lat++) // iNUserLats <= 181
{
for (int sensor = 0; sensor < 20; sensor++)
{
if (pData->pRawVals[sensor][lat] != NULL)
{
delete[] pData->pRawVals[sensor][lat];
pData->pRawVals[sensor][lat] = NULL;
} // end if
} // end for
}
...
for (int sensor = 0; sensor < 20; sensor++)
{
for (int lat = 0; lat < 46; lat++)
{
if (pData->pMaxPlaneRawPlanes[sensor][lat] != NULL)
{
delete[] pData->pMaxPlaneRawPlanes[sensor][lat];
pData->pMaxPlaneRawPlanes[sensor][lat] = NULL;
} // end if
} // end for
} // end for
Hope I got enough of the code posted. At any rate, when deallocating pMaxPlaneRawPlanes on a second pass through the code, it turns out that certain elements of that array overlap elements of pRawVals and the deallocation causes a crash - appears that those locations may have been freed previously but I can't seem to point the finger at exactly how it's happening.
Any hints on how to narrow that kind of thing down? I run development on Windows 7 Ultimate 64 bit, but the app is compiled for 32 bit.
Thanks

Answer 1

You may go out of range in any of your array, or you may go out of range elsewhere.
If you are using Visual Studio 2019, or you are using gcc or clang, you can give ASan (Address Sanitizer) a try. (VS2019 link)
Otherwise you can try Application Verifier with Full Heap check enabled.
It is also possible to use custom allocation and allocate memory the way that it will access violation on out of bounds, even if off by one. It is essentially duplicating Application Verifier for particular allocations.
Using std::array or std::vector recommended in comments will also help making fewer errors that lead to heap corruption in the first place. vector manages deallocations automatically, and also in debug builds may have checks for out-of-range errors.