5/22 TIL: Processes, Contrapositive, etc.

--Systems--

Processes

A process is an instance of an executing program; each process has a unique process id & its parent process id
Virtual memory of a process is logically divided into:
- Text initialized & uninitialized
- Data
- Stack - a series of frames with a new frame being added as a function is invoked & removed when the function returns; each frame contains local variables, function arguments, and called linkage information for a single function implication
- Heap
Command line arguments supplied when a program is invoked are made available via argc and argv arguments to the main function


#include<unistd.h>

int proc_id = getpid();

int par_proc_id = getppid();

Memory Allocation


malloc() // memory allocation

calloc() // contiguous allocation

free() // de-allocate

realloc() // re-allocate

// example

int* ptr

int num=8;

ptr = (int*)malloc(num*sizeof(int))

System Limits

SUSV3 (Single Unix Specification V3) adds a lot of new functions into C/C++ library
SUSV3 specifies limits that an implementations may enforce and system options that an implementation may support


#include <limits.h>

LONG_MIN, LONG_MAX, CHAR_MIN, CHAR_MAX // etc

--Discrete Math--

if p then q (p → q)

p → q ≡ ~p V q

~(p → q) ≡ ~(~p V q) ≡ (~~p ʌ ~q) ≡ p ʌ ~q

apply DeMorgan's Law
the only scenario where p → q is false is when p is T and q is F. Negating that p → q would be F. So this is equivalent to p ʌ ~q where p is T and q is F.

Contrapositive of a conditional

p → q ≡ ~q → ~p because