Push Pointer of Element into Stack

Question

I'm trying to push a pointer of my element into the stack so it would return a pointer instead of the element.

Based on my limited understanding it's returning the element but not the pointer.

typedef struct Stack
{
    int capacity;
    int size;
    TLDNode* elements;
}Stack;


void push(Stack *S,TLDNode *element)
{

    S->elements = element;
    S->size = S->size + 1;
    return;
}



 Stack *S;
    S = (Stack *)malloc(sizeof(Stack));
    S->elements = ( TLDNode *)malloc(sizeof( TLDNode)*100);
    S->size = 0;
    S->capacity = 100;

    PUSHTOSTACK(tld->head, S);

void PUSHTOSTACK(TLDNode *root,Stack *S) {

    PUSHTOSTACK(S,root);

}

S->size = S->size + 1; can be simplified to S->size += 1; or even S->size++; — DaoWen
– DaoWen, Commented Oct 23, 2015 at 1:32

DaoWen · Accepted Answer · 2015-10-23 01:21:00Z

1

Your elements member of your stack struct has type TLDNode*, which is equivalent to an array of TLDNodes. What you want is an array of pointers to TLDNodes, so you need another * in there:

typedef struct Stack
{
    int capacity;
    int size;
    TLDNode** elements;
}Stack;

Technically this is just a pointer to a pointer to a TLDNode, but this is basically equivalent to an array of pointers, as demonstrated by the following code snippet:

TLDNode *node_array[10]; // Array of 10 pointers to TLDNodes
TLDNode **elements = node_array; // node_array is assignable to elements

edited Oct 23, 2015 at 1:21

answered Oct 23, 2015 at 1:16

DaoWen

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2 Comments

DaoWen Over a year ago

@FlyingAtom - You don't need to (and arguably shouldn't) cast the result of malloc in C. Try this: S->elements = malloc(sizeof(*S->elements)*100);

DaoWen Over a year ago

@FlyingAtom - You should really only ask one question per question.... But your types obviously don't match. They don't match because you're trying to replace the whole elements array with a single element. What you probably want to do is set the last element in the array to the given element. S->elements[S->size-1] = element;

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