Stack

We can use the Stack structure as a LIFO container that is used to implement BFS and routines to determine strongly connected components.

To instantiate a Stack, we use the function newStack to return a pointer to newly allocated Stack that currently holds noVertex

Construction

Stack *s = newStack();

Push/Pop

To Add vertices to the stack, we simple call the companion functions pushStack/popStack. Following conventions, pushing to the stack will add a new element on top whereas popping the stack will remove the top element from the stack and then return that element.

pushStack(s, 10);
pushStack(s, 40);
pushStack(s, 13);

Vertex v0 = popStack(s);
Vertex v1 = popStack(s);
Vertex v2 = popStack(s);

Freeing Memory

When it comes to freeing the memory that has been allocated on subsequent calls to pushStack, we can use handy utility function freeStack. This routine will remove all of the Vertex objects that currently exist in the stack, freeing them as they are released.

pushStack(s, 1);
pushStack(s, 2);
pushStack(s, 3);

printf("Size of stack %d\n", stackSize(s)); // 3

freeStack(s);

printf("Size of stack %d\n", stackSize(s)); // 0

pushStack(s, 10);

This routine is useful when we want a fresh start with the stack and we don't want any memory leaks in our program. If you no longer wish to use the Stack *s, consider calling the releaseStack function to also clean up the space allocated by newStack and to nullify the pointer s.

releaseStack(&s) // s freed and set to NULL here

releaseStack will free all of the nodes populating the stack and also release the memory pointed to by s. This shall be called when your program no longer needs to use the Stack.

Inquiry

We can inspect the state of our Stack using the utility functions stackSize and printStack.