getpid/getppid系統調用

功能描述：
getpid返回當前進程標識，getppid返回父進程標識。

 
用法： 
#include <sys/types.h>
#include <unistd.h>

pid_t getpid(void);
pid_t getppid(void);

例子：

#include <stdlib.h>
#include <stdio.h>
#include <sys/types.h>

int main(void)
{
 pid_t pid;
 printf("Before fork .../n");
 
 switch(pid = fork()) {
  case -1:
   printf("Fock call fail/n");
   exit(1);
   
  case 0:
   printf("The pid of child is: %d/n", getpid());
   printf("The pid of child's parent is: %d/n", getppid());
   printf("Child exiting.../n");
   exit(0);
  
  default:
   printf("The pid of parent is: %d/n", getpid());
   printf("the pid of parent's child is: %d/n", pid);
 }
 
 printf("After fork, program exiting.../n");
 exit(0);
}