Segmentation fault - reading array of initialized pointers - c++

Question

could you help me with little problem?
I have following class;
class Link
{
private:
Demand *demand_[NUMBER_OF_CORES][NUMBER_OF_SLICES];
public:
Link()
{
for (int i = 0; i < NUMBER_OF_CORES; i++)
{
for (int j = 0; j < NUMBER_OF_SLICES; j++)
{
demand_[i][j] = NULL;
}
}
}
int virtualPut();
}
There will be problem with demand_ array. In the constructor everything is fine, after initialization I can use if (demand_[i][j] == NULL).
Problem starts in virtualPut()
int Link::virtualPut()
{
for (int i = 0; i < NUMBER_OF_CORES; i++)
{
for (int j = 0; j < NUMBER_OF_SLICES; j++)
{
std::cout << "We're in " << i << " " << j << " \n" << std::flush;
if (demand_[i][j] == NULL) //SEGMENTATION FAULT
{
std::cout << "EMPTY\n";
}
}
}
}
And also - if I call virtualPut() in constructor (just for test) it works fine.
But outside Link class I use.
void someFunction(Link *tab, int links)
{
tab = new Link[links];
tab[0].virtualPut(); //also just for test
}
What could be a problem here? I know that I can use vector, but that won't help me understand this memory problem.
One more thing - Dr. Memory says:
UNADDRESSABLE ACCESS: reading 0x0000000000000009-0x0000000000000011 8 byte(s)
But why?
EDIT!
Problem solved in comments, thank you

Answer 1

The code you show us is okay. I ran it on my side with huge values, and there is no Segfault.
You declared a "Demand* array of array" in your Link class, and this is a valid declaration, the memory should be allocated.
What I do suspect is that NUMBER_OF_CORES and/or NUMBER_OF_SLICES doesn't have the same value in the code where you defines the Link class and in the code where you defined the virtualPut method.
Something like :
#define NUMBER_OF_CORES 10
#define NUMBER_OF_SLICES 10
class Link
{
private:
Demand *demand_[NUMBER_OF_CORES][NUMBER_OF_SLICES];
...
}
and
#define NUMBER_OF_CORES 5000
#define NUMBER_OF_SLICES 5000
int Link::virtualPut()
{
for (int i = 0; i < NUMBER_OF_CORES; i++)
{
for (int j = 0; j < NUMBER_OF_SLICES; j++)
{
// here you will have buffer overflow
...
}
What I would do :
use std::vector
probably use a single entry array, and wrap it up
don't use #define, it's messy
don't use arrays, it generates buffer overflow
That would be something like this :
class Link
{
private:
std::vector<Demand*> demand_;
const int NUMBER_OF_CORES = 10;
const int NUMBER_OF_SLICES = 50;
private:
int getIdx(int i, int j)
{
return i*NUMBER_OF_SLICES + j;
}
public:
Link()
{
demand_.resize(NUMBER_OF_CORES * NUMBER_OF_SLICES);
for (int i = 0; i < NUMBER_OF_CORES; i++)
{
for (int j = 0; j < NUMBER_OF_SLICES; j++)
{
demand_[getIdx(i,j)] = NULL;
}
}
}
int virtualPut();
};
Note : additionaly, you showed us a virtualPut() that should return an int but doesn't.