fork函数分析举例

as we all know the exec() family function can only take the executable file to create a new process which replace the original one even the PID is the same to the original one, in contrast the fork funciton create a whole new process .the fork() function duplicates the current process , creating a new entry in the process table with many of the same attributes as the current process, the new process is almost identical to the original , executing the same code but with its own data space , environment , and file descriptors ,

#include <sys/types.h>#include <unistd.h>pid_t fok(void);

call to fork in the parent returns the PID of the new child process , the new process continues to execute just link the original , with the exception that in the child process the call to fork returns 0 ,and this allows both the parent and child to determine which is which .

and a typical code fragment using fork is

pid_t new_pid;new_pid=fork();switch(new_pid){     case -1:.........break;     case 0:..........break;/*child process*/     default:.....break;/*parent process*/           }

now show you an example about it:

#include <stdio.h>#include <stdlib.h>#include <unistd.h>#include <sys/types.h>int main(){pid_t num;char * mes;int n=0;int n1=1;int n2=1;printf("hello , are you ready\n");num=fork();switch(num){case -1:{printf("error\n");break;}case 0:{mes="child";    n1=5;n=5;break;}default:{mes="parent";    n2=3;n=2;break;}}for(int i=0;i<n1;i++){printf("%s--------%d\n",mes,getpid());sleep(1);}for(int i=0;i<n2;i++){printf("%s>>%d\n",mes,getpid());sleep(1);}printf("\n");for(int i=0;i<n;i++){printf("%s---%d",mes,i);sleep(1);}return 0;}

and the result is as follows: