The ‘#ident
’ directive takes one argument, a string constant. On some systems, that string constant is copied into a special segment of the object file. On other systems, the directive is ignored. The ‘#sccs
’ directive is a synonym for ‘#ident
’.
These directives are not part of the C standard, but they are not official GNU extensions either. What historical information we have been able to find, suggests they originated with System V.
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 preprocessor 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 ‘#
’. Supposedly some old C programs contain such lines.
© Free Software Foundation
Licensed under the GNU Free Documentation License, Version 1.3.
https://gcc.gnu.org/onlinedocs/gcc-6.3.0/cpp/Other-Directives.html