How to print a pound / hash via C preprocessor?

Question

I need help doing the following:

a preprocessor macro label(x) shall output \"#x\", e.g.,

#define label(x) ...

if I call label(anam

Answer 1

I don't think you can, which is not wholly unreasonable since the output of the C preprocessor should not produce an unquoted '#' because that would indicate a pre-processor directive, and you cannot generate pre-processor directives on the fly like that.

In other words, the C preprocessor is a preprocessor for C (and C++) and not a completely general purpose tool.

Either use an alternative macro processor (m4 is the standard recommendation on Unix-like systems), or go about things differently.

For example, have the macro replacement:

#define label(x)    !@!x

Then post-process the output replacing '!@!' with '#'.

(The imake program uses a similar stunt; the C preprocessor does most of the work, but its output doesn't preserve line breaks needed by 'make', so 'imake' uses the notation '@@\' or thereabouts to indicate where line breaks need to be inserted after the C preprocessor has done its worst.)