error reallocating 2d array using realloc in c

Question

I am getting an error in a huge application that I have when I try to reallocate a 2d int array. Trying to narrow down the problem, I generated a small code only with the reallocations. ERROR :

 a.out: malloc.c:3574: mremap_chunk: Assertion ((size + offset) & (mp_.pagesize-1)) == 0' failed.

Aborted.

Relevant code:

 int main()    
 {

    int **am=NULL,size=0,ans=0,i;
    char **name=NULL;
    while(ans!=7)
    {
    printf("\n\n\t1. Add a Point \n\n\t2.Exit\n\n\t\t Enter your Choice : ");
    scanf("%d",&ans);
    switch(ans)
    {
            case 1 :
                    name=realloc(name,(size+1)*sizeof(char *));                            
                    name[size]=realloc(name[size],100*sizeof(char));                        

                    printf("\nEnter Name of Point : ");
                    scanf("%s",name[size]);

                    am=realloc(am,(size+1)*sizeof(int *));                          
                    am[size]=realloc(am[size],(size+1)*sizeof(int));                ``

                    if(size > 0 && am==NULL)
                    {
                            printf("Error : Can not Allocate Memory !");
                            break;
                    }
                    for(i=0;i<=size;i++)
                    {
                            if(i!=size)
                            {
                                    am[size][i]=INFINITE;
                                    am[i][size]=INFINITE;
                            }
                            else
                                    am[i][size]=0;
                    }
                    size++;
                    break;
            case 2 :
                    exit(0);

    }
 }

 }

Answer 1

Your first problem is here:

name=realloc(name,(size+1)*sizeof(char *));                            
name[size]=realloc(name[size],100*sizeof(char)); 

The memory returned by realloc (NULL,) is uninitialized. This means that you're passing a random pointer to the second realloc(). Use malloc() instead.

The same goes for the second pair of realloc() calls.

There is another problem here:

for(i=0;i<=size;i++)
{
  if(i!=size)
  {
    am[size][i]=INFINITE;
    am[i][size]=INFINITE;

You're accessing am[i][size] for every am[i], but only the last one will actually have that many elements. The amount allocated will grow through every round of the while loop. You need to rethink your logic.