prg13_4_1.c

配套光盘网络编程进程间的通信,网络编程进程间的通信是一本很经典的好书

#include <sys/types.h>
#include <fcntl.h>
#include <sys/stat.h>
#include <stdlib.h>
#include <sys/mman.h>

#define FILE_MODE (S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH)
int main(int argc,char **argv)
{
  int  c,fd1,fd2,flags;
  int  *ptr1,*ptr2;
  pid_t  pid;
  struct stat wstat;
  flags = O_RDWR | O_CREAT;
  int i;
  if (argc > 3)
  {
  	printf("usage %s: <name>",argv[0]);
  	exit(0);
  }
  
  while((c = getopt(argc,argv,"e")) !=-1)
  {
  	switch(c)
  	{
  		case 'e':
  			flags |= O_EXCL;
  			break;
  	}
  }
  
  shm_unlink(argv[1]);
  fd1 = shm_open(argv[1],flags,FILE_MODE);
  ftruncate(fd2,sizeof(int));
  fd2 = shm_open("/etc/motd",O_RDONLY,FILE_MODE);
  fstat(fd2,&wstat);  //获取大小信息
  
  if ((pid = fork()) == 0)
  {
    ptr2 = mmap(NULL,wstat.st_size,PROT_READ,MAP_SHARED,fd2,0);
    ptr1 = mmap(NULL,sizeof(int),PROT_READ | PROT_WRITE,
      MAP_SHARED,fd1,0);
    printf("child:shm ptr =%p,motd ptr = %p\n",ptr1,ptr2);
    sleep(5);
    printf("shared memory integer = %d\n",*ptr1);
    exit(0);
  }
  else if (pid >0)
  {
    ptr1 = mmap(NULL,sizeof(int),PROT_READ | PROT_WRITE,
      MAP_SHARED,fd1,0);
    ptr2 = mmap(NULL,wstat.st_size,PROT_READ,MAP_SHARED,fd2,0);
    printf("parent:shm ptr = %p,motd ptr = %p\n",ptr1,ptr2);
    *ptr1 = 777;
    waitpid(pid,NULL,0);
    exit(0);
  }
  else
  {
    printf("fork() is error\n");
    exit(0);
  }
}