“this” pointer in C (not C++)

Question

I\'m trying to create a stack in C for fun, and came up with the idea of using struct to represent the stack. Then I add function pointers to the struct for push() and pop()

Answer 1

In header file you can declare static this variable

static struct Stack *this;

And then in push method you can use this variable

static int push(int val) {
    if(this->current_size == this->max_size - 1)
            return 0;

    this->data[this->current_size] = val;
    (this->current_size)++;

    return 1;
}

The caveat is you have to manually set this variable through some method before you want to invoke other methods, eg:

struct Stack {
    struct Stack (*_this)(struct Stack *); // <-- we create this method
    int *data;
    int current_size;
    int max_size;
    int (*push)(int);
    int (*pop)();
};

And then we can implement _this method as

static struct Stack *_this(struct Stack *that)
{
    retrun this = that;
}

The example:

struct Stack stack1, stack2;

... some initialization ...

stack1->_this(&stack1)->push(0);
stack1->push(1);
stack1->push(2);

stack2->_this(&stack2);
stack2->push(10);
stack2->push(20);