In this particular case, calculating the year directly in your program is a better solution, as stated in the comments.
In general, though, you'll need to make run a dependency of year. Here's a solution that uses an intermediate file, which doesn't overwrite year.c, but you can modify it to overwrite if you'd like:
year.c:
#include <stdio.h>
#ifndef YEAR
#define YEAR "2013"
#endif
int main(void)
{
printf("Hello world from " YEAR "\n");
return 0;
}
Makefile:
year: run
gcc year_manip.c -o year
run:
cat year.c | sed -e 's/3/4/g' > year_manip.c
Sample session:
paul@horus:~/src/sandbox/year$ ls
Makefile year.c
paul@horus:~/src/sandbox/year$ make
cat year.c | sed -e 's/3/4/g' > year_manip.c
gcc year_manip.c -o year
paul@horus:~/src/sandbox/year$ ./year
Hello world from 2014
paul@horus:~/src/sandbox/year$
Note that this solution means your program will always compile, i.e. your run target is never up-to-date. If you made it dependent on either year.c or year_manip.c, then when 2015 came around, it still wouldn't rebuild, which is probably not what you want. You could probably do something more complicated with make, to overcome this, if necessary.
For this particular problem, when the question is purely one of pre-#defineing an identifier with a value, the answer to the linked question obviously gives a much simpler method which will work here. For more general code generation, using makefiles in this way can be useful.
