Thread: bsearch and struct **pointers

Dear fellow coders,

I've been having problems with this piece of code and I can't seem to figure out the cause. I'd really appreciate it if someone could point out why I'm getting errors here..

Code:

typedef struct {
   char *name; 
   unsigned long match_num; 
   unsigned long *match_support; 
   struct graphNode **link; 
} graphNode;

int node_compare(const void *a, const void *b) {
   return strcmp(((graphNode*)a)->name, ((graphNode*)b)->name);
}

   graphNode **NODE_INDEX = (graphNode**) malloc(SHOTGUN_READ_NUM*sizeof(graphNode*));

//SNIP

   qsort(NODE_INDEX, SHOTGUN_READ_NUM, sizeof(graphNode*), node_compare); // sort shotgun fragments by name

// SNIP

   for (count=0; count<match_count_5; count++) { 
	graphNode *a = malloc(sizeof(graphNode));
	a->name = name_array_5[count]; // points a->name to a string in memory
	graphNode *fromNode = bsearch(a, NODE_INDEX, SHOTGUN_READ_NUM, sizeof(graphNode*), node_compare);
	free(a);

//SNIP

gdb shows that in node_compare(), the values pointed to by a->name and b->name are garbage, or sometimes out of bounds.

Anyone?

i'm a beginner in this.. but i'll make a contribution anyway and see what people say..

in this line..

graphNode *a = malloc(sizeof(graphNode));

i noticed your missing your typecast?

e.g.

Code:

main()
{
   int* aPtr = NULL;
   
   aPtr = (int*)malloc(sizeof(int));
   *aPtr = 5;

   free(aPtr);
}

though looks like a and b are both void? i haven't done anything like this before. but seeing as they're both void i guess you don't need the typecast

oops. I must've missed a few casts out.. It still doesn't work though, and I think it's more to do with the fact that the node_compare function isn't working right.

Maybe I'm casting the args wrongly or something.. I'll work on it

Thanks for the reply though!

Originally Posted by ahming

i'm a beginner in this.. but i'll make a contribution anyway and see what people say..

in this line..


i noticed your missing your typecast?

e.g.

Code:

main()
{
   int* aPtr = NULL;
   
   aPtr = (int*)malloc(sizeof(int));
   *aPtr = 5;

   free(aPtr);
}

though looks like a and b are both void? i haven't done anything like this before. but seeing as they're both void i guess you don't need the typecast

wow i think this is beyond me. i'm only starting to learn this stuff plus exam on it in two weeks sorry if i couldn't help