The standard predefined macros are specified by the C and/or C++
language standards, so they are available with all
compilers that
implement those standards. Older compilers may not provide all of
them. Their names all start with double underscores.
__FILE__--------------当前文件的名字
__BASE_FILE--------假设a.h被b.c包含，那么__FILE__是a.h,__BASE_FILE__是b.c。
__LINE__--------------是当前的行数