Lecture 014

C0 Memory So Far

• Computer has one memory - array of bytes

• bytes indexed by addresses

• C0 address is 2^64 bytes

Memory Diagram

Memory diagram

• THE Heap (allocated memory): Grow from down to top

• THE Stack (local memory): Grow from top to down

• stack-overflow: when these Stack and Heap collide

• Accessing OS Memory: segmentation fault

• NULL: has segfault, NULL is address 0x0

• Code: functions

• Strings: separate memory

C0

We can use

• address of an array

• address of struct

• NULL

• address of a string

C1

• address of a function pointer

• & address-of operator

• a function called key_hash, we get the address by calling &key_hash (a function's pointer)

• type declare typedef int what-to-what-fn(int a, int b);

• type store string_to_in* F = &key_hash;*

• call function int h = (*F)("hello");'

  • writing F("hello") is incorrect since it is (F("hello"))
  • writing *F->H is acceptable

• safety: F != NULL;, & ensures \result != NULL

• use: pass function pointer on creation time of a struct (object oriented programming)

• contracts

  • for implementation, we can use these functions in contracts
  • for user interface, we CANNOT use user input function as contracts

• YOU HAVE TO DEREFERENCE BEFORE CALLING: (*F)(variable)