求大侠帮忙见见多线程拷贝文件代码出错

求大侠帮忙看看多线程拷贝文件代码出错

#include<stdio.h>

  #include<unistd.h>

  #include<fcntl.h>

  #include<sys/types.h>

  #include<sys/stat.h>

  #include<pthread.h>

  #include<string.h>

  

  #define SPATH "/root/Desktop/pthread/1G.rar"

  #define DPATH "/root/Desktop/1G1.rar"

  #define SIZE 1024

  #define NUM_THREAD 5

  

  int get_size(char *filename);

  void* threadCp(void *arg);

  int i_thread=0;

  

  typedef struct Cp_INFO

  {

      int i_num;

  }info;

  

  int get_size(char *filename)

  {

      struct stat st;

      memset(&st,0,sizeof(st));

      stat(filename,&st);

      return st.st_size;

  }

  void* threadCp(void *arg)

  {

      info info1=*((info*)arg);

      int in=0;

      int out=0;

      int size=0;

      int rlen=0;

      char buffer[SIZE]={'\0'};

      in=open(SPATH,O_RDONLY);

      if(-1==in)

      {

          printf("Open File error!\n");

      }

      out=creat(DPATH,O_WRONLY);

      if(-1==out)

      {

        printf("Create File error!\n");

      }

      size=get_size(SPATH);

      printf("i_num=%d\n",info1.i_num);

      printf("size*i_thread/NUM_THREAD=%d\n",size*i_thread/NUM_THREAD);

      lseek(in,size*i_thread/NUM_THREAD,SEEK_SET);

      lseek(out,size*i_thread/NUM_THREAD,SEEK_SET);

      int len=0;

      int total=0;

      while((rlen=read(in,buffer,sizeof(buffer)))>0)

      {

          write(out,buffer,rlen);

          total+=rlen;

          if(total>size/NUM_THREAD)

          {

              break;

          }

      }

      close(in);

      close(out);

  }

  

  int main()

  {

	pthread_t pid[NUM_THREAD];

      info c_info;

      int i=0;

      int j=0;

      /*int out=creat(DPATH,S_IWUSR);

      if(-1==out)

      {

          printf("Create File error!\n");

          return -1;

      }*/

  

     for(i=0;i<NUM_THREAD;i++)

      {

          i_thread=i;

          c_info.i_num=i;

          printf("info_inum=%d\n",c_info.i_num);

          pthread_create(&pid[i],NULL,threadCp,(void*)&c_info);

      }

  

      for(j=0;j<NUM_THREAD;j++)

      {

          pthread_join(pid[j],NULL);

      }

      printf("copy file finish!\n");

      return 0;

  }

这段代码运行后把一个1.2G的文件复制成314M样子的文件，看了很久没看出问题所在，请大侠帮忙看看问题在哪？小弟谢谢大家了
------解决思路----------------------
这个应该是要加线程锁