getpid/getppid系统调用

功能描述：
getpid返回当前进程标识，getppid返回父进程标识。

 
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);
}