Include from preprocessor macro - c

Question

I am trying include a file constructed from pre-processor macros, but running into a wall due to rules regarding tokens, it seems. I used the answer here as a reference: Concatenate string in C #include filename, but my case differs in that there are decimal points in the define I am using to construct my include. This is what I have currently that will not get through the preprocessor stage:
main.c:
#include <stdio.h>
#include <stdlib.h>
#define VERSION 1.1.0
#define STRINGIFY(arg) #arg
#define INCLUDE_HELPER(arg) STRINGIFY(other_ ##arg.h)
#define INCLUDE_THIS(arg) INCLUDE_HELPER(arg)
#include INCLUDE_THIS(VERSION)
int main(int argc, char **argv) {
printf(INCLUDE_THIS(VERSION));
fflush(stdout);
#if defined (SUCCESS)
printf("\nSUCCESS!\n");
#endif
return EXIT_SUCCESS;
}
other_1.1.0.h:
#define SUCCESS
Were I to use #define VERSION 1_1_0 and renamed the header accordingly it would work (but not viable for my use as I have no control over the name of the header files the actual project uses), but 1.1.0 is not a valid preprocessor token.
EDIT:
After a bit more digging through the documentation, I see that 1.1.0 is a valid preprocessing number; it is the resulting concatenation of other_1.1.0 that is invalid. Regardless, the issue of not being able to construct the include remains.

Answer 1

It's easy once you stop thinking about token concatenation. Stringification works with any sequence of tokens, so there is no need to force its argument into being a single token. You do need an extra indirection so that the argument is expanded, but that's normal.
The only trick is to write the sequence without whitespace, which is what ID is for:
#define STRINGIFY(arg) STRINGIFY_(arg)
#define STRINGIFY_(arg) #arg
#define ID(x) x
#define VERSION 1.1.0
#include STRINGIFY(ID(other_)VERSION.h)
See https://stackoverflow.com/a/32077478/1566221 for a longer explanation.

Answer 2

With some experimentation, I came up with a solution that, while not ideal, could be workable.
#define VERSION _1.1.0
#define STRINGIFY(arg) #arg
#define INCLUDE_HELPER(arg) STRINGIFY(other ##arg.h)
#define INCLUDE_THIS(arg) INCLUDE_HELPER(arg)
#include INCLUDE_THIS(VERSION)
Rather than pasting other_ and 1.1.0 together, I am pasting other and _1.1.0. I am not sure why this is acceptable as the resulting token is the same, but there it is.
I would still prefer to have a solution that allows me to just define the version number without the underscore, so I will hold off on accepting this answer in case someone can come up with a more elegant solution (and works for people who don't happen to need an underscore anyways)

Answer 3

If you are passing -DVERSION=1.1.0 as a compile-line parameter, rather than hard-wiring it in the source code, then there's nothing to stop you passing a second define using make or the shell to do the concatenation. For example, in a makefile, you might have:
VERSION = 1.1.0
VERSION_HEADER = other_${VERSION}.h
CFLAGS += -DVERSION=${VERSION} -DVERSION_HEADER=${VERSION_HEADER}
and then:
#include <stdio.h>
#include <stdlib.h>
#define STRINGIFY(arg) #arg
#define INCLUDE_HELPER(arg) STRINGIFY(arg)
#define INCLUDE_THIS(arg) INCLUDE_HELPER(arg)
#include INCLUDE_THIS(VERSION_HEADER)
int main(void)
{
printf("%s\n", INCLUDE_THIS(VERSION));
#if defined (SUCCESS)
printf("SUCCESS!\n");
#endif
return EXIT_SUCCESS;
}
which is basically your code with the #define VERSION line removed, and using the stringified version of VERSION_HEADER instead of trying to construct the header name in the source code. You might want to use:
#ifndef VERSION
#define VERSION 1.1.0
#endif
#ifndef VERSION_HEADER
#define VERSION_HEADER other_1.1.0.h
#endif
for some suitable default fallback version in case the person running the compilation doesn't specify the information on the command line. Or you might use #error You did not set -DVERSION=x.y.z on the command line instead of setting the default value.
When compiled (source file hdr59.c):
$ gcc -O3 -g -std=c11 -Wall -Wextra -Werror -DVERSION=1.1.0 \
> -DVERSION_HEADER=other_1.1.0.h hdr59.c -o hdr59
$ ./hdr59
1.1.0
SUCCESS!
$
I would put the three lines of macro and the #include line into a separate small header so that it can be included when the version header is needed. If the default setting is required too, then that adds to the importance of putting the code into a separate header for reuse. The program's source code might contain:
#include "other_version.h"
and that header would arrange to include the correct file, more or less as shown.