Linux-fork () function, with code comments

////main.c//Project_c////Created by Lijinxu on 16/8/13.//copyright©2016 year Lijinxu-neu. All rights reserved.//#include<stdio.h>intMainintargcConst Char*argv[])    {pid_t fpid; /*Test Fork Part 1*/        intCount =0; printf ("The main process ' s ID is%d\n", Getpid ()); Fpid=Fork (); //1.fork://Fork creates a process that is almost identical to the original process through a system call.    However, depending on the parameters, two processes can also perform different functions. //after a process calls fork, the system assigns resources, such as data storage and code space, to the new process first. Then copy the original values (not exactly the same)//The fork call returns two times at a time:printf"fpid:%d\n", Fpid); if(Fpid <0)//Fpid < 0: Error occurredprintf"Error in fork\n"); Else if(Fpid = =0){//Fpid = = 0: Child process returned 0printf"Child process ' s ID is%d\n", Getpid ()); printf ("My Parent process ' s ID is%d\n", Getppid ()); Count+=1; }Else{//fpid > 0: Parent process returns the ID of the newly created child processprintf"Parent process ' s ID is%d\n", Getpid ()); printf ("My Parent process ' s ID is%d\n", Getppid ()); Count+= -; }    //2.fpid: In fact, the relationship between processes, like a linked list.    The parent process returns the ID of the child process that was pointed to, and no process after the child process returns 0. //3.getpid: Each process has a unique (non-identical) process identifier, which can be obtained through GETPID (). //3.1.getppid: Gets the PID of the parent process. //4. Execution order: There is no fixed order of execution, sequencing according to the system's process scheduling strategy. //5. Interpretation of the results of implementation: 4868-4867 (PAR) (Main), 4870 (child), 0. //when the printout is printed, it is found that the PID = 1 of the parent process is printed in the child process (as indicated by the previous result: it should be 4867). This is because the parent process (main process) has exited after execution, and the parent process of the child process is set to P1,p1 never die .printf"Count =%d\n", Count); /*Test Fork Part 2*/     for(inti =0; I <3; i + +) {Fpid=Fork (); if(Fpid = =0) printf ("child\n"); Else if(Fpid >0) printf ("father\n"); Else{printf ("error\n"); }    }    /*i = 0, 1, 2 father father father son son                       Father son son father father son Son father son sum up the law, for this n-cycle situation, the number of times to execute the printf function is (1+2+4+......+2n-1), the created Wahabbi          The number of threads is 1+2+4+......+2n-1. */    return 0;}

The following transfers from http://blog.csdn.net/jason314/article/details/5640969

Another code is as follows:

 for (i=0;i<2; i++) {      pid_t fpid=fork ();   after execution, i=0,fpid=3225      if(fpid==0)         printf ("  %d child  %4d%4d%4d/n", I,getppid (), Getpid (), fpid);       Else          printf ("%d parent%4d%4d%4d/n", I,getppid (), Getpid (), fpid) ;  }  

Clearly see the relationship between processes:

Linux-fork () function, with code comments