Pointer

& returns the memory address of the object

• called "address of" operator
  • Therefore, this gets applied to the value to get the memory address
• ie. p = &c;

* either:

1. declares a pointer variable, or
   • ex. int *p;
2. dereferences an existing pointer (indirection through a pointer)

• called "indirection" or "dereferencing" operator
  • Therefore, this gets applied to the pointer to get the value in storage
• int a = 5 then int *ptr = &a;
  • this means "locate" the address where a is stored, and assign its value to ptr
    • In other words, the value of ptr will now be the address where a is stored.
• *ptr = 8
  • this means take the address of ptr, "locate" that address in memory, and set its value to 8.
• int *ptr
  • "ptr is a pointer that points to an object of type int", or simply: "ptr is a pointer to int."

If p points to the integer x, then *p can occur in any context where x could, so:

*p = *p + 10;
// is the same as
x = x + 10;

• This picture shows how a pointer references a storage location, which holds a variable c. When we use the & operator, we are talking about the place where c is stored. When we use the * operator, we are talking about the variable c itself.

• each pointer points to a specific data type, which is why we declare a pointer variable int *p;

  • The exception is "pointer to void", which can hold any kind of pointer, but cannot be dereferenced itself.

• C does not implicitly initialize storage duration of memory locations. Therefore, we should be careful that the address that the pointer points to is valid.

  • For this reason, some suggest initializing pointers to NULL (null pointer/null reference)
  • null pointer shown as 0x00000000

• Like other languages, manipulating a function argument will have no effect on the original variable that was passed to the function. This is because when we pass an argument, a copy is made and we are merely mutating the copy.

  - However, we are also able to call a function, passing in the variable's *address* as the argument `passByAddr(&x)`.
  

  from within the function, if we change the value like so *m = 14. this changes the value at the address, so outside the function we'll notice that the value changed