c - Understanding how fork() and wait() work together -

this isn't in code review because not understand full concept of code start with. if should still moved let me know.

i have code , explain thoughts on it, , hoping can tell me going wrong or getting confused @ because still not sure occurring.

#include <sys/types.h> #include <stdio.h> #include <unistd.h> int main()    {    pid_t pid, pid1;    pid = fork();     if (pid < 0) {       fprintf (stderr, “fork() failed\n”);       return(1);    }    else if (pid == 0) {       pid1 = getpid();       printf (“pid = %d\n”, pid); //       printf (“pid1 = %d\n”, pid1); // b    }    else {       pid1 = getpid();       printf (“pid = %d\n”, pid); // c       printf (“pid1 = %d\n”, pid1); // d       wait (null);    }    return 0; } 

from understand, have 2 process id's, parent (pid) , child (pid1). once call pid = fork(), believe child initiated , given id of 0, while parent get's id of child, let 1337. pid = 1337 , pid1 = 0.

so skip first if no error has occurred (pid < 0), skip second if since pid not equal 0, , enter final if c print 1337 , d pint out 0.

this waits until child done, think.

after that, assume copied process (fork()) run else if (pid == 0) confused on why, because pid still 1337..

tldr: if third if should executing first, how second if, if logic wrong please correct me.

a fork creates makes (near-perfect) copy of running process. 1 difference, surmised return value of fork() itself. so, assuming fork works have 2 processes executing same code. one, child, takes if (pid == 0) ... path, while parent takes else... path. have no information order in 2 processes work. maybe child goes first, maybe parent, maybe half way through take turns, maybe have 2 processors , run together...

imagine have program written on piece of paper , following along finger, sliding down page. when fork, take paper copier, make copy, put both pieces of paper on table, put index finger each hand on 1 of pieces, move both fingers, each sliding down own sheet of paper.