CODEWITHSUNDEEP
c++
Boby
Boby

Reputation: 125

Stack around variable is corrupted error

I am writing the following code and I am getting Stack around variable is corrupted error. I have checked similar posts but couldn't relate the problems. I am also rather new to C++. Here is my code.

///CLASS DEFINITION
class Trellis{

    private:
        int m;
        int Nstates;
        int StateTransition[];

    public:
        Trellis(); 
        Trellis(int M);
};

Here is the definition of methods

Trellis::Trellis(int M){
    m = M;
    Nstates = pow(2, M - 1);

    for (int i = 0; i < Nstates; i++){
        StateTransition[i] = i;
    }
}

int main() {

Trellis Tu = Trellis(3);

return 0; }

The error I get is Run-Time Check Failure #2-Stack around variuble 'Tu' was corrupted;

Upvotes: 0

Views: 462

Answers (2)

Marco A.
Marco A.

Reputation: 43662

Flexible array members were a C99 feature which allowed you to do something like

struct header {
    size_t len;
    unsigned char data[];
};

and, provided that you had a proper memory layout, you could access and write to the data array.

In your case you're not providing any memory for your StateTransition variable and thus overwriting some other stack data.

You had better doing something like

class Trellis
{
private:
  int m;
  int Nstates;
  int *StateTransition; // Pointer

public:
  Trellis(); 
  Trellis(int M);
  ~Trellis();
};
Trellis::Trellis() : StateTransition(0) {
}
Trellis::Trellis(int M) : StateTransition(0)
{
  m = M;
  Nstates = pow(2, M - 1);

  StateTransition = new int[Nstates]; // Allocate memory

  for (int i = 0; i < Nstates; i++)
  {
    StateTransition[i] = i;
  }
}

Trellis::~Trellis() {
    if(StateTransition != 0)
        delete[] StateTransition; // Always be a good citizen
}

And as for the rule of three, you might also want to write a copy constructor.

Upvotes: 0

Paul Evans
Paul Evans

Reputation: 27567

You're not allocating any memory for StateTransition, you want something like:

StateTransition = new int[Nstates];

before your for loop in the ctor.

Upvotes: 4

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