最近考试用$fread$然后对拍的时候发现拍出来的文件不一样，但是关掉$freopne$之后运行输出的是一样的，有人知道为什么吗（

const int BUF_SIZE = 1 << 12;
    
char buf[BUF_SIZE] , *buf_s = buf , *buf_t = buf + 1;
    
#define PTR_NEXT() \
{ \
    buf_s ++; \
    if(buf_s == buf_t) \
    { \
        buf_s = buf; \
        buf_t = buf + fread(buf , 1 , BUF_SIZE , stdin); \
    } \
}
    
template <typename _n_> void mian(_n_ & _x_){
    while(*buf_s != '-' && !isdigit(*buf_s)) PTR_NEXT();
    bool register _nega_ = false; if(*buf_s == '-'){ _nega_ = true; PTR_NEXT(); }
    _x_ = 0; while(isdigit(*buf_s)){ _x_ = _x_ * 10 + *buf_s - '0'; PTR_NEXT(); } if(_nega_) _x_ = -_x_;
}