pkutaj

The aim of this page📝 is to learn SICP in public. I will publish my notes as I go. Maybe reduntant. But I'm blogging mainly for myself, for the imagined community. No AI as a writing assistant (yes AI a way to talk to text_books), just a morning routine of keyboard, teacher, Anki Notes and a small deep work.

1. Links

• https://www.youtube.com/playlist?list=PLE18841CABEA24090
• https://gist.github.com/pkutaj/59b1ff40b5a7367d2ebdbd92dd395cde (self)

2. Steps

pkutaj

high address ┌────────────┐
             │   stack    │  ← grows downward, per-thread
             │     ↓      │
             │   (gap)    │
             │     ↑      │
             │    heap    │  ← grows upward, shared across threads
             │────────────│
             │    BSS     │  uninitialised globals
             │   data     │  initialised globals
             │   text     │  code

pkutaj

thread-1 stack    thread-2 stack
    │                  │
    ▼                  ▼
 [frame A]          [frame X]
    │                  │
    └──► heap ◄────────┘
         [obj-1][obj-2][obj-3]

pkutaj

void create_typist(int uses_nvim) {
  int wpm = 150;
  char name[4] = {'p', 'a', 'u', 'l'};
}

pkutaj

Lower Address <--------------------------------------------------------> Higher Address
             *<pointer>
+----------+-----------+-----------+---------+---------+---------+---------+----------+
| <return> | uses_nvim |    wpm    | name[0] | name[1] | name[2] | name[3] |   ...    |
+----------+-----------+-----------+---------+---------+---------+---------+----------+
|   ...    |     1     |    150    |   'p'   |   'a'   |   'u'   |   'l'   |   ...    |
+----------+-----------+-----------+---------+---------+---------+---------+----------+
| 0xFEFC   | 0xFF00    | 0xFF04    | 0xFF08  | 0xFF0C  | 0xFF10  | 0xFF14  |   0xFF18 |
+----------+-----------+-----------+---------+---------+---------+---------+----------+
\____________________________________________________________________________________/

pkutaj

Type	Size
char	1
unsigned char	1
signed char	1
short	2
unsigned short	2
int	2,4
unsigned int	2,4
long	4,8

pkutaj

#include <stdlib.h>
#include <stdio.h>

int main() {
    int *p = (int *)malloc(sizeof(int));  // allocate on heap
    *p = 42;
    printf("%d\n", *p);
    free(p);                              // must always free
    return 0;
}

pkutaj

heap (graph of pointers)          wire (flat byte sequence)

 [obj-A] ──ptr──► [obj-B]
      └──ptr──► [obj-C]    →→→    [ A | B | C | ... ]

  virtual addresses              no addresses, just values
  process-local                  portable, self-contained

pkutaj

Year	Milestone
1957	FORTRAN — static allocation only, no heap
1960	LISP — first language with dynamic allocation + GC
1960	ALGOL 60 — introduced stack frames as a formal concept
1966	DRAM invented by Robert Dennard at IBM
1972	C — direct control via malloc()/free()

pkutaj

# include <stdio.h>

int* dangerous() {
  int x = 42;
  return &x;
}

int main() {
  int* p = dangerous();
  printf("print pointer of dangerious: %d\n", *p);