Generic Stack Implementation in C

Stack : Last in First Out (LIFO) dynamic set. An array based implementation is done.

This directory contains following files:

• stack.h: declarations of all the functions on stack Type declarations:

  • byte: byte is equivalent to unsigned char (which occupies 1 Byte).
  • struct Stack:
    • top: This stores number of elements present in the stack (which is also equal to the index of top element).
    • storage: an array of bytes to store all stack elements.
    • elemSize: size (in bytes) of one element of stack.
    • maxElements: Maximum elements that can be inserted in the stack.

  Methods defined:

  • init: Initializes the stack of a particular data-type. It takes size of the type and max elements as parameters.
  • isEmpty: Checks if the stack is empty.
  • size: Returns number of elements present in the stack.
  • push: Pushes an element into the stack. It takes a void pointer as a element. This pointer must point to element to be inserted.
  • pop: Removes the top element from the stack and returns a void pointer to the removed value.
  • top: Returns a void pointer to the value at top of stack without actually removing the element.
  • destroy: Destroys the memory allocated to stack.

• stack.c: Implementation of functions defined in stack.h

  • init: Uses malloc to allocate (elemSize*maxElements) bytes to storage. Also makes top to 0.
  • isEmpty: Checks if top is 0.
  • size: Returns top.
  • push: First checks if space is available. Then copies the element given in parameter byte by byte on top of stack. Increases top by 1.
  • pop: First checks if stack is empty. Then calls top fn to get top element, decreases top by 1 and returns the element.
  • top: Checks if stack is empty. Allocates elemSize bytes to a new element. Copies elemSize bytes from top of stack into element and then returns a void pointer to it.
  • destroy: frees the memory allocated to storage.

• stacktest.c: Checks all the methods defined using a stack of integers and a stack of doubles.

• Makefile: make compiles everything. Other options: make run and make compile.

Merits and Demerits

Merits:

• A stack for any data type can be created by just passing the size of the data type as a parameter.
• All the functions are generic. They can work with any data type.

Demerits:

• There is no type checking. There is no way to check if the element given to push is of same type as of stack. However this can not be avoided without losing genericity.

Reasons for using this approach

This approach is inspired from stack based memory allocation used in almost all processors. This approach at one side is as low-level as it can get (using bytes) and on another side is generic enough to work for any data type.

References

• Introduction to Algorithms, Cormen
• The C Programming Language, Kernighan and Ritchie
• Stack Based Memory Allocation