How to create a macro string

Question

I'm trying to define a string macro before compiling my C code. I've tried something like:

#include <stdio.h>

int main(void) {
    printf("%s", AMEM);
    return 0;
}

and I've tried to compile with:

gcc -D AMEM="Deus Abencoa" file.c

But I keep getting this message:

file.c:5:15: note: in expansion of macro ‘AMEM’
  printf("%s", AMEM);
               ^
<command-line>:0:4: note: each undeclared identifier is reported only once for each function it appears in
file.c:5:15: note: in expansion of macro ‘AMEM’
printf("%s", AMEM);

Any idea of how to put it to work?

Note that the space between -D and macro=value is immaterial; it works with and without that space. — Jonathan Leffler
– Jonathan Leffler, Commented Dec 6, 2013 at 22:14

mirabilos · Accepted Answer · 2013-12-06 22:22:18Z

4

Your shell interprets (“eats up”) the double-quotes. Since they need to be part of the cpp macro (as the C compiler requires them to form a string), you must pass them to the compiler driver, which means escaping them from the shell. Try this:

gcc -D'AMEM="Deos Abencoa"' file.c

Or this (commonly seen with GNU autoconf):

gcc -DAMEM=\"Deos\ Abencoa\" file.c

Do note that there is no space after -D either.

edited Dec 6, 2013 at 22:22

answered Dec 6, 2013 at 22:10

mirabilos

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5 Comments

Jonathan Leffler Over a year ago

The space after the -D is optional and most often omitted but not necessary.

mirabilos Over a year ago

What I meant was: note that my (working) way does not have a space. I know systems that require there be no space after cpp options like -D and -I.

Jonathan Leffler Over a year ago

Which systems require 'no space'?

mirabilos Over a year ago

I saw GCC choke (on MirBSD, but I think it should also do on GNU/Linux) when the space after -I was missing. I cannot state offhead which one it was for -D as it's been a very long time since I last accidentally had a space.

Jim Balter Over a year ago

I deleted my comment, as it was off-base. Please adjust your answer to say something like "your shell interprets the double quotes itself and doesn't pass them to gcc".

Jonathan Leffler · Accepted Answer · 2013-12-06 22:11:00Z

1

gcc -D AMEM='"Deus Abencoa"' file.c

The shell removes the single quotes, leaving the double quotes visible to the compiler. Before, the shell removed the double quotes.

answered Dec 6, 2013 at 22:11

Jonathan Leffler

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