Value inside pointer changes

[xaviergxf]

Hi,

I'm using vs2010 and debugging this piece of code:.

void InsertAndShift(Node* pInto, const K& pKey, const V& pValue, const int& Idx)
{
int j_calc;
for(int j=pInto->CountKeys;j > Idx;j--)
{
j_calc = j-1;
pInto->Keys[j] = pInto->Keys[j_calc];
pInto->Values[j] = pInto->Values[j_calc];
}
pInto->Keys[Idx] = pKey;
pInto->Values[Idx] = pValue;
pInto->CountKeys++;
}

When the debbugger is before the first line of the function, CountKeys has 2 as value, but when i press f10 and step over it has the value of 4192516. The pInto parameter still has the same address. Any one has a clue of what's going on?

Thanks

[Disch]

On what line does the value of CountKeys change?

If Keys and/or Values are arrays, and you are stepping outside the bounds of those arrays, you might be corrupting memory and overwriting the contents of CountKeys by mistake.

[xaviergxf]

It changes in : int j_calc;

I was looking into the disassembly and here's when it changes:

81: void InsertAndShift(Node* pInto, const K& pKey, const V& pValue, const int& Idx)
82: {
00222980 push ebp
00222981 mov ebp,esp
00222983 sub esp,0E4h
00222989 push ebx
0022298A push esi
0022298B push edi
0022298C push ecx
---change>>>0022298D lea edi,[ebp-0E4h]

[vlad from moscow]

It seems that you overwrite memory. Are you sure that

pInto->Keys[ pInto->CountKeys ];

or

pInto->Values[ pInto->CountKeys ]

are valid array elements?

[xaviergxf]

The problem is on the beginning of the function, when suddenly pInto->CountKeys changes from 2 to 4193076.

[Disch]

That seems extremely unlikely.

Can you upload the full source somewhere (and steps to reproduce) so we can try it out?

[threeright]

for(int j=pInto->CountKeys;j > Idx;j--)
{
    j_calc = j-1;
    pInto->Keys[j] = pInto->Keys[j_calc];
    pInto->Values[j] = pInto->Values[j_calc];
}

When you do j=CountKeys are you making sure that "CountKeys" is < (size of array)-1?

[cire]

If the contents of the memory pInto points to is changed when the stack is modified, that suggests that pInto is pointing at a variable on the stack that has gone out of scope.

[xaviergxf]

Hi cire,

That's exactly what was happening.

Thanks a lot!