代码有问题 ，段错误

include

include

include

include

include

include

include

include

int main(int argc,char *argv[])
{

char buf[1024];
int fd=open(argv[1],O_RDONLY);
if(fd==-1)
{
perror("open source file failed!");
exit(1);
}

int fd1=open(argv[2],O_WRONLY |O_CREAT| O_EXCL,0777);
if(fd1==-1)
{
perror("open tap file failed!");
exit(1);
}

int len=lseek(fd,0,SEEK_END);

if(len==-1)
{
perror("lseek failed!");
exit(1);
}
int block_size=len%4+1;
// char *buf=NULL;
//char buf[1024];
int i=0;
int pid;
for(i=0;i<3;i++)
{
pid=fork();
if(pid==0)
break;

}
int n=read(fd,buf,block_size);
if(n<0)
{
perror("read failed!");
exit(0);
}
int m=write(fd1,buf,n);

if(pid>0)
while(wait(NULL));

//free(buf);
close(fd);
close(fd1);
return 0；

}