memcpy和mmap

/*
author:justinzhang
email:uestczhangchao@gmail.com
time:2012-8-22 18:50:23:
desc: a buggy program from bbs.qshpan.com, i use strerror(errno) to locate
the problem, the problem is that i didn't give the second command line arguments.
 After making it running properly, i add some exception handling code:)
*/
#include<errno.h>
#include<sys/mman.h>
#include<sys/types.h>
#include<fcntl.h>
#include<unistd.h>
#include<string.h>
#include<stdio.h>
#include<sys/stat.h>
#include<stdlib.h>
typedef struct
{
  char name[4];
  int age;
}people;
main(int argc,char** argv)
{
   int fd ,i;
   people *p_map;
   char temp;
   if(argc < 2){
       printf("usage %s filename\n",argv[0]);
       exit(EXIT_FAILURE);
   }
   fd=open(argv[1],O_CREAT|O_RDWR|O_TRUNC,00777);
   if(fd == -1)
   {
       printf("error:%s\n",strerror(errno));
    exit(EXIT_FAILURE);
   }
   lseek(fd,sizeof(people)*5-1,SEEK_SET);
   write(fd,"",1);
   p_map=(people*)mmap(NULL,sizeof(people)*10,PROT_READ|PROT_WRITE,MAP_SHARED,fd,0);
   close(fd);
   temp='a';
   for(i=0;i<10;i++)
   {
        temp += 1;
    printf("%s\n",strerror(errno));
        memcpy((*(p_map+i)).name,&temp,2);
        (*(p_map+i)).age=20+i;
   }
    printf("initialize over!\n");
    sleep(10);
    munmap(p_map,sizeof(people)*10);
    printf("umap ok!\n");
}