Tutorials:Pointers

Make sure to understand value types or read this first: Value types

Pointers are integers who's size is the base word size of the process and store an address in that process. That is in a 16 bit process a pointer is a WORD (16 bit), in a 32 bit process a pointer is a DWORD (32 bit), and in a 64 bit process a pointer is a QWORD (64 bit).

16 bit

WORD : int16/short

32 bit

DWORD : int32/int

64 bit

QWORD : int64/long

In programs and programming simply using only integers and floating point values really isn't feasible with complex objects. So the concept of an object in memory was seen as a must. This is where pointers come in. They simply point to an object in memory, hence the name. Even strings are implemented with pointers to the series of characters in memory, though most high-level languages don't make you aware of that fact.

In the ANSI C there is no string type just character arrays, and they use a Null-terminated format.

Objects in memory

Now let's say we have some code that declares a player object and its setup like this:

• Player : object
  • Name : string
  • Health : integer
  • Coins : integer
  • Coordinates : object
    • X : float
    • Z : float
    • Y : float
  • Inventory : array - Array of item objects, having the item and item count.

So in a 32 bit process in memory the player object could get assembled some thing like this:

• Process.exe+123ABC : pointer : DWORD - Player base.
  • [Process.exe+123ABC]+10 : pointer : DWORD - Pointer to where the Name string is stored in memory.
    • [[Process.exe+123ABC]+10]+4 : string : 256 bytes - The Name value, as a null (0x0) ended string.
  • [Process.exe+123ABC]+14 : integer : DWORD - Health value.
  • [Process.exe+123ABC]+18 : integer : DWORD - Coins value.
  • [Process.exe+123ABC]+1C : pointer : DWORD - Pointer to where the Coordinates object is stored in memory.
    • [[Process.exe+123ABC]+1C]+10 : float : DWORD - X coordinate.
    • [[Process.exe+123ABC]+1C]+14 : float : DWORD - Z coordinate.
    • [[Process.exe+123ABC]+1C]+18 : float : DWORD - Y coordinate.
  • [Process.exe+123ABC]+20 : pointer : DWORD - Pointer to where the Inventory array starts in memory.
    • [[Process.exe+123ABC]+20]+XX*4 : pointer : DWORD - Pointer to where the inventory array item number XX is stored in memory.
      • [[[Process.exe+123ABC]+20]+XX*4]+4 : integer : DWORD - The inventory item Count value.
      • [[[Process.exe+123ABC]+20]+XX*4]+8 : pointer : DWORD - Pointer to where item object is stored in memory.

And in a 64 bit process in memory the player object could get assembled some thing like this:

• Process.exe+123ABC : pointer : QWORD - Player base.
  • [Process.exe+123ABC]+10 : pointer : QWORD - Pointer to where the Name string is stored in memory.
    • [[Process.exe+123ABC]+10]+8 : string : 256 bytes - The Name value, as a null (0x0) ended string.
  • [Process.exe+123ABC]+18 : integer : DWORD - Health value.
  • [Process.exe+123ABC]+1C : integer : DWORD - Coins value.
  • [Process.exe+123ABC]+20 : pointer : QWORD - Pointer to where the Coordinates object is stored in memory.
    • [[Process.exe+123ABC]+20]+10 : float : DWORD - X coordinate.
    • [[Process.exe+123ABC]+20]+14 : float : DWORD - Z coordinate.
    • [[Process.exe+123ABC]+20]+18 : float : DWORD - Y coordinate.
  • [Process.exe+123ABC]+28 : pointer : QWORD - Pointer to where the Inventory array starts in memory.
    • [[Process.exe+123ABC]+28]+XX*8 : pointer : QWORD - Pointer to where the inventory array item number XX is stored in memory.
      • [[[Process.exe+123ABC]+28]+XX*8]+4 : integer : DWORD - The inventory item Count value.
      • [[[Process.exe+123ABC]+28]+XX*8]+8 : pointer : DWORD - Pointer to where item object is stored in memory.

But if we had a Player object that contains an Actor object, it might get assembled some thing like this in a 32bit process:

• Process.exe+123ABC : pointer : DWORD - Player base.
  • [Process.exe+123ABC]+4 : pointer : DWORD - Actor base.
    • [[Process.exe+123ABC]+4]+10 : pointer : DWORD - Pointer to where the Name string is stored in memory.
      • [[[Process.exe+123ABC]+4]+10]+4 : string : 256 bytes - The Name value, as a null (0x0) ended string.
    • [[Process.exe+123ABC]+4]+14 : integer : DWORD - Health value.
    • [[Process.exe+123ABC]+4]+18 : integer : DWORD - Coins value.
    • ...

And the more complex the object structure the more complex the pointer structure.

Example of multi-level pointers

Check out step 8 of the Cheat Engine Tutorial for an example of multi-level pointers.

• Cheat Engine Tutorial Guide (x32)
  • Cheat Engine Tutorial Guide (x32) - Step 8
• Cheat Engine Tutorial Guide (x64)
  • Cheat Engine Tutorial Guide (x64) - Step 8

See also

• Tutorials

External links

• wikipedia.org/wiki/Pointer_(computer_programming)