Thread: Is this analogy for pointers (*operator), addresses (& operator) and variables valid?

A pointer is an address.

Code:

int *ptr_num, num;
// ptr_num is of type pointer to int, num is of type int. Illustration of why not do declare multiple variable at same time perhaps
ptr_num = # // until here ptr_num would have been some random address, now stored is the addres of num
num = 5; // you know this.
*ptr_num = 6; // now num = 6, we dereferenced the pointer with the dereference symbol. This says I want what is pointed at, not the pointer
// itself. ptr_num is the address of num. It adds a layer of indirection.

^ I think I should have written pointer variable in my title?

Is there a difference between a pointer variable and a pointer?

Does a pointer consist of a pointer variable + an address?

I've seen the author of my book use both terms to use different things scattered throughout the chapter.

Originally Posted by potomac

^ I think I should have written pointer variable in my title?

Is there a difference between a pointer variable and a pointer?

Does a pointer consist of a pointer variable + an address?

The terms 'pointer variable' and 'pointer' are interchangeable.

No a pointer is a variable like any other. The only difference is rather than store data there, we store the address of some data. To get to the data being pointed at the pointer has to be dereferenced with the * operator.

In C all parameter passing is 'by value'. This means that when you pass something to a function, the function actually gets a copy of data passed.

Code:

void foo( int a )
{
   a = 5;
}

int main()
{
   int num = 0;
   foo(num);
   // what is num here??
   return 0;
}

Where the comment is num has two possible values, they are 0 or 5. Which is it and why?
It's 0. In main we set num to zero and then we pass a copy of num to foo, so the changes made in foo to num are not reflected back to main. foo was never working with num, it was working with a copy of num.

Code:

void bar( int* ptr )
{
   *ptr = 5;
}

int main()
{
   int num = 0;
   bar(&num); // bar expects type pointer to int passed to it, so we pass the address of num
   // what is num here?
   return 0;
}

here again the same two possible values for num at the comment are 0 or 5. This time it's 5. Why?
Again we pass a copy ( all passing in C is 'by value' ). Our pointer is copied and passed to bar. in the function the copied pointer is dereferenced to get to the object being pointed at, and the assignment is made to that memory location. We have just simulated passing by reference by passing the address of an int rather than by passing the int itself. Because we passed an address the changes we made to the object at that address percolate back up to main. This is what Salem means by don't copy your house, send the address of your house.

A value is a chunk of memory interpreted as a particular type.
A variable is a named address.
A pointer is a variable whose value is interpreted as an address.
That's it.
Your analogies are useless.
Why add a layer of obfuscation over such an incredibly simple concept?