对输入操作符进行重载

istream& read_word(istream&is,char* buffer,int max)

{

 is.width(max);//read at most max-1 characters in the next>>

 is>>buffer;//read whitespace-terminated word,add zero after the last character read into buffer

 return is;

}

合理地设置独享istream的宽度能够避免>>操作导致缓冲区溢出