valid int pointers

[khulme]

these are marked as invalid C++ code in my documentation. not sure why. would appreciate any insight.

int ptr = &num1;

int ptr = int *num1;

float num1 = &ptr2;

[Moschops]

int ptr = &num1;
&num1 gives the address of the object num1 i.e. it gives a pointer. You cannot assign a pointer to an int.

int ptr = int *num1;
This is just wrong syntax. It's akin to int a = float b;; just wrong.

float num1 = &ptr2;
This is the first one again with float instead of int. You can't assign a pointer to a float.

[atropos]

For the first line, you're attempting to assign an address to an int, which is a no-no. (An address, while represented by an integer, is not an integer.)

In the second line, you're trying to assign a pointer to an int, also bad.

Third part is the same explanation as the first.

If you want to define an alias to a variable, use this notation:

int num1 = 2;
int &int_ref = num1;

[khulme]

thanks Moschops and atropos.
this concept is not sinking in for me.
i am confused by the use of * and &.
i thought that if i wanted to indicate the address of num1, i would write &num1. and if i wanted to indicate the value in num1, i would write *num1.
but it looks like this labeling is different from int *num1. what does int *num1 indicate then? an address? or a value?

[Moschops]

int num1;
Make an int, name it num1. It has some random value.

int * num1;
Make a pointer-to-int, name it num1. It has some random value.

int ptr = 7;
Make an int, name it ptr, and set its value to seven.

int ptr = int *num1;
Make an int, name it ptr, and set its value to... oh, hang on, this is nonsense and the compiler will reject it.

[atropos]

khulme wrote:

what does int *num1 indicate then? an address? or a value?

int * num1; declares a pointer-to-int called 'num1'.

example:

//...
int num = 2;   //integer variable defined
int * ptr = NULL; //pointer-to-int declared and initialized to NULL (it's good practice to initialize all variables)
ptr = #   //OK, since '&num' is the address(pointer) to 'num'
std::cout << "Num is: " << num << std::endl;  // displays '2'
std::cout << "Ptr points to: " << *ptr << std::endl; // displays value pointed to by ptr, which is the value of num (which of course, is '2')
std::cout << "Num is at memory address: " << ptr << std::endl; //displays the address of 'num' 

[Lowest0ne]

^^

std::cout << "Memory address of ptr: " << &ptr << std::endl;

int ** ptrPtr = &ptr;  // a pointer to a pointer

std::cout << "Memory address of ptr: " << ptrPtr << std::endl;
std::cout << "Value of ptr: " << *ptrPtr << std::endl; // the address of num
std::cout << "Value of num: " << **ptrPtr << std::endl;

&(*++argv)[1]; // The first important address of a command line argument

[ResidentBiscuit]

What you're talking about is what gets most people confused when they first get into pointers.

int *ptr = &bar;
*ptr = 12;

The two astericks (*) there are simply just the same symbol used for different tasks. They mean different things, and do different things. Why they did this? I don't know, but it tends to confused people.

Anyway, line one is just a pointer declaration and initialization (you should always initialize your pointer right away). The second line is what's called dereferencing the pointer, using that same asterik, and what that does is returns the value at the address that the pointer is pointing. In this case, it returns the value that bar holds.

[khulme]

thank you ResidentBiscuit, LowestOne, atropos and Moschops.
extremely helpful.
it seems more logical to me to define the pointer with the * after the int, rather than before the name... as in int* ptr rather than int *ptr.
anyway, thanks.

[ResidentBiscuit]

That's how I like putting them, but it doesn't matter. As long as its somewhere in between the type and identifier.

[Moschops]

it seems more logical to me to define the pointer with the * after the int, rather than before the name... as in int* ptr rather than int *ptr.

Do it however you like; just be careful not to get caught out with

int* a, b; // a is a pointer, b is is not

[khulme]

got it. thanks everyone.