POSIX 父子进程协同一例

子进程生成fibnacii 父进程输出
#include <sys/types.h>
#include <sys/shm.h>
#include <sys/stat.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#define MAX_SEQUENCE 10
typedef struct {
   int fib_sequence[MAX_SEQUENCE];
   int sequence_size;
        }shared_data;
int main(int arg, char* argv[])
{
 if (arg != 2)
  exit(-1); 
 
 pid_t pid; 
 int segment_id, n;
 shared_data* seq;
  
 if (!(segment_id = shmget(IPC_PRIVATE, sizeof(shared_data),  S_IRUSR|S_IWUSR)))
 {
  printf("fail to allocate memory!\n");
  fprintf(stderr,"fail to allocate memory!");
  exit(-1);
 }
 if ((seq = (shared_data*)shmat(segment_id, 0, 0)) == (shared_data *)-1) 
 {
  printf("fail to attach to segment\n");                
  fprintf(stderr,"fail to attach to segment %d\n",segment_id);
                exit(-1);
        }
 
 
 n = atoi(argv[1]);
 pid = fork();
 
 if (pid < 0)
 {
  printf("fail to set a new process!\n");
  fprintf(stderr, "Fork failed!");
  exit(-1);
 }
 else if (pid == 0)
 {
  int i, fir, secd, fib;
  
  if (n <= MAX_SEQUENCE)
  {  
   if (n == 1)
   {
    seq->fib_sequence[0] = 0;  
    seq->sequence_size = 1; 
   }
   else if (n == 2)
   {
    seq->fib_sequence[0] = 0;
    seq->fib_sequence[1] = 1;  
    seq->sequence_size = 2; 
   }
   else 
   {
    fir = 0;
    secd = 1;
    seq->fib_sequence[0] = 0;
    seq->fib_sequence[1] = 1;
    seq->sequence_size = n;
    for (i = 3; i <= n; i++)
    {
   
     fib = fir + secd;
     fir = secd;
     secd = fib;
     seq->fib_sequence[i-1] = fib;
    }
   
   }
  }
  else
  {
   exit(-1);
  }
 }
 else
 {
  wait(NULL);
  
  if (n > MAX_SEQUENCE) 
  {
   printf("overflow!\n");
   exit(-1);
  }
  
  else
  {
   int i = 0;
   while (i < n)
   {
    printf("%4d", seq->fib_sequence[i++]);
   }
   printf("\n%d", seq->sequence_size);
   exit(0);
  }
 }
}