Problems with implementing a stack in C

Question

I tried to implement to stack in C. Here is my code, I ran the code, the code ended with:

Thread 1: EXC_BAD_ACCESS error

I am so confused, don't know what went wrong, can anyone debug y code? Thanks!

And I have one more question, why command+k key didn't work for me? I have to indent line by line.

#include <stdio.h>
#include <stdlib.h>   
#define init_size 10
#define increment 1

typedef struct sqStack
{
    int* top;
    int* base;
    int stack_size;
} sqStack;

int init_stack(sqStack* sq)
{
    if(sq->base==NULL)
    {
        sq->base = (int*)malloc(init_size*sizeof(int));//Thread 1: EXC_BAD_ACCESS 
    }
    if(sq->base==NULL) exit(-1);
    sq->stack_size=init_size;
    sq->top=sq->base;
    return 1;
}

int push(sqStack* sq, int e)
{
    if(sq==NULL) exit(-1);
    if(sq->top-sq->base==sq->stack_size)
    {
        int* q = (int*)realloc(sq->base,  
        (init_size+increment)*sizeof(int));
        if(q==NULL) exit(-1);
        else
        {
            sq->base=q;
            sq->stack_size += increment;
            sq->top=sq->base+sq->stack_size;
        }
        *sq->top++=e;
    }
    return 1;
}

int pop(sqStack* sq,int*e)
{
    if(sq==NULL) exit(-1);  
    if(sq->base==sq->top)  exit(-1);   
    sq->top-=1;   
    *e=*sq->top;   
    return 1;    
}

int empty(sqStack* sq)
{
    if(sq->base==sq->top) return 1;
    else return 0;
}


int main()
{
    sqStack* sq=NULL;
    init_stack(sq);
    push(sq,1);
    int *e=(int*)malloc(sizeof(int));
    pop(sq,e);
    printf("%d\n",*e);
    return 0;
}

You are passing a NULL pointer to init_stack where you try to dereference it. — Osiris
– Osiris, Commented Jan 27, 2019 at 16:54

Yunbin Liu · Accepted Answer · 2019-01-27 17:28:55Z

1

In function int init_stack(sqStack* sq) the

 if(sq->base==NULL)
   {
     sq->base = (int*)malloc(init_size*sizeof(int));//Thread 1: EXC_BAD_ACCESS 
   }

should be:

sq->base = (int*)malloc(init_size*sizeof(int));//Thread 1: EXC_BAD_ACCESS

In function int push(sqStack* sq, int e)

the

    }
     *sq->top++=e;
}
return 1;
}

should be

    }
  }
  *sq->top++=e;
  return 1;
}

In function int main()

the is not need use int *e=(int*)malloc(sizeof(int)); just use int e;

the

sqStack* sq=NULL;
init_stack(sq);
push(sq,1);
int *e=(int*)malloc(sizeof(int));
pop(sq,e);
printf("%d\n",*e);

should be

sqStack sq;
init_stack(&sq);
push(&sq,1);
int e;
pop(sq,&e);
printf("%d\n",e);

The following code could work:

#include <stdio.h>
#include <stdlib.h>
#define init_size 10
#define increment 1

typedef struct sqStack {
  int* top;
  int* base;
  int stack_size;
} sqStack;

int init_stack(sqStack* sq) {
  sq->base = (int*)malloc(init_size * sizeof(int));
  if (sq->base == NULL) exit(-1);
  sq->stack_size = init_size;
  sq->top = sq->base;
  return 1;
}

int push(sqStack* sq, int e) {
  if (sq == NULL) exit(-1);
  if (sq->top - sq->base == sq->stack_size) {
    int* q = (int*)realloc(sq->base, (init_size + increment) * sizeof(int));
    if (q == NULL)
      exit(-1);
    else {
      sq->base = q;
      sq->stack_size += increment;
      sq->top = sq->base + sq->stack_size;
    }
  }
  *sq->top++ = e;
  return 1;
}

int pop(sqStack* sq, int* e) {
  if (sq == NULL) exit(-1);
  if (sq->base == sq->top) exit(-1);
  sq->top -= 1;
  *e = *sq->top;
  return 1;
}

int empty(sqStack* sq) {
  if (sq->base == sq->top)
    return 1;
  else
    return 0;
}

int main() {
  sqStack sq;
  init_stack(&sq);
  push(&sq, 1);
  int e;
  pop(&sq, &e);
  printf("%d\n", e);
  return 0;
}

answered Jan 27, 2019 at 17:28

Yunbin Liu

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3 Comments

Yunbin Liu Over a year ago

Before use a pointer, you must init like sqStack* sq=&stack; not sqStack* sq=NULL; @Liu

Liu Over a year ago

what is the difference between sqStack* sq and sqStack &sq?? Why the later works? And isn't sqStack &sq=NULL too??

Yunbin Liu Over a year ago

sqStack& sq; is reference use in c++, sqStack* sq; is pointer use in c and c++, sqStack* sq=NULL; sq point NULL, sqStack stack; sqStack* sq = &stack; sq point stack

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