重定向 printf 时遇到的小问题

uestczcl

在重定向 printf 时，为什么这个 FILE 没有用到，它应该是指定某一个文件的啊，这里它并没有指定！ 为什么呢？

csmjmcc

在《stdio.h》中如是说：
    * writes the character specified by c (converted to an unsigned char) to
    * the output stream pointed to by stream, at the position indicated by the
    * asociated file position indicator (if defined), and advances the
    * indicator appropriately. If the file position indicator is not defined,
    * the character is appended to the output stream.