Error "read access violation" appears randomly

CyxouD

Hello
I was making my hashtable visual project based on linear probing and got some issue.
I have a variable N,which was declared privately,that describes how many elements in hashtable, then i have a method **put **,where i get problem when incrementing N(N++) exactly after or in more put after resizing hashtable with method resize(I think they are connected with this issue may be?) .In debugger it is "Exception at 0x5028bff6, code: 0xc0000005: read access violation at: 0x0, flags=0x0 (first chance)" and variable N,as i said,is 2 or 3(N=2,N=3). I would appreciate any help.

Added:Hmm.. if i made this process manually(putting elements) and initialize with N=0 in constr then the same exception appears when N=2 in String 18 of method resize : temp->put(keys[i],vals[i]);

void put(QString key,QString val)
    {
        if (val==NULL)
        {
            deleteKey(key);
            return;
        }

        **if (N>=M/2) resize(2*M);**

        int i;
        for (i=(qHash(key) & 0x7fffffff) % M;keys[i]!=NULL;i=(i+1) % M) {
          if (QString::compare(keys[i],key)==0) {vals[i]=val; return;}
        }
        keys[i]=key;
        vals[i]=val;
        N++; //here is exception

    } 


void resize(int capacity)
    {
        LinearProbingHashST *temp=new LinearProbingHashST;
        temp->init(capacity);
        for (int i=0;i<M;i++) {
            if (keys[i]!=NULL){
               temp->put(this->keys[i],this->vals[i]);
            }
       }
        keys=temp->keys;
        keys=temp->vals;
        M=temp->M;
        delete temp;

    }

public:
    LinearProbingHashST()
    {
      init(INIT_CAPACITY);
    }

    void init(int capacity)
    {
        M=capacity;
        keys=new QString[M];
        vals=new QString[M];
        N=0;
    }

SGaist

Hi and welcome to devnet,

Do you ensure that M has a correct value ? How do you do the resize ?

alex_malyu

@CyxouD said:

 keys=temp->keys;
    keys=temp->vals;

Above code seems contains undesired features.
In any case such code complexity requires compilable simple test case.