Thread: Stack Implementation No Errors

Hello everyone,

I am writing some code to implement a stack in C. For this is am using this website article as a guide https://www.cs.bu.edu/teaching/c/stack/array/

I was testing the code as I go and add the features and I noticed I did not get any error while trying to access an item from an index beyond the the allocation of the stack. For example I have a stack of 2 elements and I still can access elements at index 500. (I was expecting segmentation here)

These are my files:

stack.h

Code:

#define STACK_MIN_CAPACITY 1 /* minimum capacity for the stack */


/*general enumerators and types. */
#ifndef CORE_H
#define    CORE_H
    typedef enum bool {FALSE, TRUE} Bool;
    typedef enum error {NO_ERRORS, ERROR} Error;
#endif

/* stack realated definitions */
#ifndef STACK_H
#define STACK_H

/* type definitions */
typedef char StackItem;
typedef struct stack{
    StackItem * items;
    int top;
    int capacity;
} Stack;

/*function prototypes */
Bool stackInitialize(Stack *);
void stackTerminate(Stack *);
Bool stackExpand(Stack *);
Bool stackPush(Stack *, StackItem);
StackItem stackPop(Stack *);
StackItem stackPeek(Stack *);
Bool stackIsEmpty(Stack *);

#endif

stack.c

Code:

/********************************************************************/
#include <stdio.h>
#include <stdlib.h>
#include "stack.h"
/********************************************************************/

/********************************************************************
 Purpose    : Initializes a Stack
*********************************************************************/
Bool stackInitialize(Stack * stack){

    StackItem * items;
    items = (StackItem *) malloc(sizeof(StackItem) * STACK_MIN_CAPACITY);

    if(items == NULL){
        fprintf(stderr, "%s\n","Could not allocate memory");
        return FALSE ;
    }else{
        stack->items = items;
        stack->capacity = STACK_MIN_CAPACITY;
        stack->top = -1;
        return TRUE;
    }
}

/********************************************************************
 Purpose    : Terminates a Stack
*********************************************************************/
void stackTerminate(Stack * stack){

    free(stack->items);

    stack->items = NULL;
    stack->capacity = 0;
    stack->top = -1;
}


/********************************************************************
 Purpose    : Expands a Stack to hold more items
*********************************************************************/
Bool stackExpand(Stack * stack){

    StackItem * temp = NULL;
    int newSize = stack->capacity * 2;

    temp = (StackItem *) realloc(stack->items,
                                 sizeof(stack->items[0]) * newSize);
    if(temp == NULL){
        fprintf(stderr, "%s\n", "Stack could not be expanded");
        return FALSE;
    }else{
        stack->capacity = newSize;
        stack->items = temp;
        return TRUE;
    }
}

/********************************************************************
 Purpose    : Pushes element to the stack
*********************************************************************/
Bool stackPush(Stack * stack, StackItem item){
    Bool success;

    if(stack->top >= stack->capacity - 1){
        success = stackExpand(stack);
    }else{
    }

    if(success){
        stack->items[++stack->top] = item;
        return TRUE;
    }else{
        fprintf(stderr, "%s\n","Could not add element to stack");
        return FALSE;
    }
}

test.c

Code:

#import <stdio.h>
#import "stack.h"

int main(int argc, char const *argv[]){

    Stack stack;
    stackInitialize(&stack);
    
    /*Add a few items and check them */
    stackPush(&stack, 'A');
    stackPush(&stack, 'B');

    printf("%c\n", stack.items[0] );
    printf("%c\n", stack.items[500] ); /*expected an error as well*/
    
    return 0;
}

Thanks a lot in advance for the help.

Thanks a lot for the reply Salem,

I guess C can do a lot of stuff with memory if I am not careful. Since this is a stack I will not give the users the option to access the items this was just me debugging and trying to triple check. I just need to add the procedures: stackPush(), StackPop(), stackPeek().

Thanks a lot for the help.