Other Directives - Red Hat ENTERPRISE LINUX 3 - USING CPP Using Instructions

Chapter 8.

Other Directives

The directive takes one argument, a string constant. On some systems, that string constant is
#ident
copied into a special segment of the object file. On other systems, the directive is ignored.
This directive is not part of the C standard, but it is not an official GNU extension either. We believe
it came from System V.
The directive is recognized on some systems, because it appears in their header files. It is a very
#sccs
old, obscure, extension which we did not invent, and we have been unable to find any documentation
of what it should do, so GCC simply ignores it.
The null directive consists of a followed by a newline, with only whitespace (including comments)
#
in between. A null directive is understood as a preprocessing directive but has no effect on the pre-
processor output. The primary significance of the existence of the null directive is that an input line
consisting of just a will produce no output, rather than a line of output containing just a . Suppos-
# #
edly some old C programs contain such lines.