CODEWITHSUNDEEP
cpointersstructdynamic-memory-allocation
optimusfrenk
optimusfrenk

Reputation: 1321

segmentation fault during the use of an array of pointer to structures

I have to save in an array the address of some data. Every data is a structure of type "dagNode". To do my work I visit a list, and I count the number of data that I want to record its address so I allocate the right space in the memory, and finally I re-visit the list and save the address of some data.

    struct dagNode *buildBST(struct dagNode *rootList){
    struct dagNode *head, **xTest;
    head = rootList;
    int numXtest=0;

    rootList = nextNode(TYPE_XTEST, rootList);

    while ( !IS_TERMINATED( rootList ) ){   // first visit
        numXtest++;
        rootList = nextNode(TYPE_XTEST, rootList); }

    xTest = (struct dagNode **) malloc( sizeof(struct dagNode ) * numXtest);
    int i=0; rootList = nextNode(TYPE_XTEST, head);

    for(i=0; i<numXtest; i++){      // second visit, saving the address of some datas
        rootList = nextNode(TYPE_XTEST, rootList);
        xTest[i] = rootList; i++;
    >>> printf("t=%d,val=%d\t", xTest[i]->nodeType, xTest[i]->val); } // segmentation fault

    return head;
    }

EDIT:

    struct dagNode *nextNode(int typeOfNextNode, struct dagNode *node){
        if (IS_TERMINATED(node)){   return node;    }
        node = node->next;
        if (typeOfNextNode == TYPE_EDGE_OR_GAP){
            while (!IS_TERMINATED(node) && !IS_AN_EDGE(node) && !IS_A_GAP(node)){
                node = node->next;  }
               }else
        {
            while (!IS_TERMINATED(node) && (node->nodeType != typeOfNextNode)){
                node = node->next;}
        }
        return node;    }

Upvotes: 0

Views: 235

Answers (3)

Lundin
Lundin

Reputation: 215305

I'm sorry but this post does not answer the question. I merely want to give you an example of an alternative coding style. Pick up what you like from it.

I haven't changed the meaning of the code, except for the removal of the most obvious bugs already pointed out in other answers/comments.

#include <stdio.h>
#include <stdlib.h>

typedef struct
{
  ...
} dagNode;

dagNode* buildBST (dagNode* rootList)
{
  dagNode*  head;
  dagNode** xTest;
  int numXtest=0;
  int i=0;

  head = rootList;
  rootList = nextNode(TYPE_XTEST, rootList);

  while (!IS_TERMINATED(rootList))               // first visit
  {
    numXtest++;
    rootList = nextNode(TYPE_XTEST, rootList);
  }

  xTest = malloc(sizeof(dagNode) * numXtest);
  rootList = nextNode(TYPE_XTEST, head);

  for(i=0; i<numXtest; i++)                      // second visit, saving the address of some datas
  {      
    rootList = nextNode(TYPE_XTEST, rootList);
    xTest[i] = rootList;

    printf("t=%d,val=%d\t", 
           xTest[i]->nodeType,
           xTest[i]->val);
  }

  return head;
}


dagNode *nextNode (int typeOfNextNode, dagNode *node)
{
  if (IS_TERMINATED(node))
  {
    return node;
  }

  node = node->next;

  if (typeOfNextNode == TYPE_EDGE_OR_GAP)
  {
    while ( !IS_TERMINATED(node) &&
            !IS_AN_EDGE(node) &&
            !IS_A_GAP(node) )
    {
      node = node->next;
    }
  }
  else
  {
    while ( !IS_TERMINATED(node) &&
            (node->nodeType != typeOfNextNode) )
    {
      node = node->next;
    }
  }

  return node;
}

Upvotes: 0

UmNyobe
UmNyobe

Reputation: 22920

nextNode() seems to be the obvious culprit.

Edit: Note that you are also incrementing i twice per iterations. This will certainly crash.

Upvotes: 2

Blagovest Buyukliev
Blagovest Buyukliev

Reputation: 43558

There is a mismatch between the type of the xTest pointer and the size you allocate in malloc. If xTest is of type struct dagNode **, the proper allocation should be:

xTest = malloc(sizeof(struct dagNode *) * numXtest);

Probably you want to allocate numXtest pointers to a struct, not numXtest structs.

Upvotes: 1

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