The standard C headers names use the form name.h. The C++ versions of these headers are named cname the C++ versions remove the .h suffix and precede the name by the letter c. Thec indicates that the header originally comes from the C library. Hence, cctype has the same contents as ctype.h, but in a form that is appropriate for C++ programs. In particular, the names defined in the cname headers are defined inside the std namespace, whereas those defined in the .h versions are not. C++ Primer 4th
我觉得记住这个规则就足够了,初学者很多头文件也用不上,要用的时候msdn上查一下就行了