Generating `#define`s from a macro

Question

// define 31:
#define f_Q31(x)                      f_Q(31,x)
#define q31_F(x)                      q_F(31,x)
#define CHECK_Q31(q,def)              CHECK_Q(31,q,def)
// define 25:
#define f_Q25(x)                      f_Q(25,x)
#define q25_F(x)                      q_F(25,x)
#define CHECK_Q25(q,def)              CHECK_Q(25,q,def)
// etc.

Can the above be generalized, like so:

#define SUPPORT_TYPE(N) something?

Adding a new type would then be a one line:

#define SUPPORT_TYPE_Q31   SUPPORT_TYPE(31)
#define SUPPORT_TYPE_Q25   SUPPORT_TYPE(25)

preprocessor only does 1 pass so you'll have to find another way. — Jean-François Fabre, Feb 02 '17 at 12:59
What [crazy](http://stackoverflow.com/q/41998251/1870232) [project](http://stackoverflow.com/q/41998931/1870232) are you on ? This is the third macros related doubt of your in a day. May be tell us why you think macros are the best for these ? — P0W, Feb 02 '17 at 13:02
It's time for you to create your own code generation script. Use your favorite scripting language to parse the source first, and generate the code you are after. — StoryTeller - Unslander Monica, Feb 02 '17 at 13:03
@P0W I think the questions were mostly usefull for the comunity. — Danijel, Feb 02 '17 at 13:05
@Danijel - The previous questions weren't all that bad. Neither is this one. But the resounding answer is simply "you can't". Use an external tool to generate the code. — StoryTeller - Unslander Monica, Feb 02 '17 at 13:06
@StoryTeller Agree, it's time for a script. Let's see where the project goes in the next days... — Danijel, Feb 02 '17 at 13:06

score 3 · Accepted Answer · answered Feb 02 '17 at 13:44

Preprocessor only has one pass, so you cannot generate #define statements with other #define statements.

You could use a small script (python comes to mind, surprisingly :)) to do what you want:

text="""// define {0}:
#define f_Q{0}(x)                      f_Q({0},x)
#define q{0}_F(x)                      q_F({0},x)
#define CHECK_Q{0}(q,def)              CHECK_Q({0},q,def)
"""

for i in (25,31):
    print(text.format(i))

when running this script it generates:

// define 25:
#define f_Q25(x)                      f_Q(25,x)
#define q25_F(x)                      q_F(25,x)
#define CHECK_Q25(q,def)              CHECK_Q(25,q,def)

// define 31:
#define f_Q31(x)                      f_Q(31,x)
#define q31_F(x)                      q_F(31,x)
#define CHECK_Q31(q,def)              CHECK_Q(31,q,def)

Agreed. And, @Danijel, there are lots [more alternatives](https://stackoverflow.com/q/396644/2877364) if you need more scaffolding, including [my personal favorite](https://stackoverflow.com/a/15027444/2877364) :) . — cxw, Feb 02 '17 at 13:48

Generating `#define`s from a macro

1 Answers1