What's the difference between _Exit() and _exit()?

Question

In answer to this question, some people have said to use _Exit() and others have said to use _exit(). Could someone explain the difference (if any) between the two, and the origins of both?

Answer 1

Right from the man page here:

The function _Exit() is equivalent to _exit().

Although in C++11, it is standardized as either std::_Exit or std::quick_exit. According to Mike Seymour here.

Answer 2

_Exit(2) is from C99. _exit(2) is from POSIX. At least, according to the manpage I have installed here.

They are entirely equivalent.