释放大量指针时的分段错误

Question

My code runs with no errors on small files. But I get segmfault on large inputs (millions line). Please see some of the code below:

element* unionFind(void *data)
{
    element *retVal = NULL;
    retVal = (element *)malloc(sizeof(element));
    retVal->data = data;
    retVal->rank = 0;
    retVal->leader = retVal;
    return retVal;
}

Main:
...

int main (int argc, char* argv[])
{   
char str[2048]; 
char* v_S = NULL; 
struct set *s_v = NULL;

* count number of lines in input

long *v_L = (long *)malloc(sizeof(long)*ct_lines);
element **v = malloc(sizeof(element)*ct_lines) ;

while(fgets(str,sizeof(str),fp) != NULL)
{
     v_S = strtok(str,":");        

     v_L[i] = atol(v_S);
         v[i] = unionFind(&v_L[i]);
     s_v = add_vertex(v_L[i], v[i]);

     i++;
}

fclose(fp);

for (i = 0; i < ct_lines; i++) //Here segfault
    {
    free(v[i]); v[i] = NULL;
    }

free(v); v = NULL;
free(v_L); v_L = NULL;

}

Answer 1

after each malloc you should check whether malloc has returned NULL( which means memory could not be allocated as heap is full). If it returns NULL, generally error message is printed. And if still you want to allocate memory you will have to retry after freeing up some already allocated memory.

As your program fails for large files, no need of reading code in detail, it must be failing since its running out of free memory and malloc is returning NULL and then you are trying to save structure elements at NULL address in top function findUnion.