c - Generate #ifdef, #endif clause with another macro -

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i'm having problem in program i'm working on. i'm trying in --help display features compiled in or not. however, there quite alot of these , "normal" way verbose. e.g.:

#ifdef have_foo static const bool have_foo = true; #else static const bool have_foo = false; #endif printf("support foo: %s\n", have_foo ? "yes" : "no");

now, since have every feature, loads of lines, not want.

so thought i'd write macros it:

#define _supp(x) #ifdef have_##x \ static const bool _##x##_supp = true; \ #else \ static const bool _##x##_supp = false; \ #endif  #define _printsupp(var, name, desc) printf("\t%s - %s: %s\n", name, desc, _##var##_supp ? "yes" : "no")

however, there issue here. macro expanded single line, , preprocessor chokes on this. there way generate macro actual newlines inbetween, or possible evaluate #ifdef on single line?

if, instead of not defining have_foo, define 0, can do:

const struct {     bool present;     const char *name; } features[nfeatures] = {     {have_foo, "foo"},     {have_bar, "bar"},     ... };  (size_t i=0; < nfeatures; i++)     if (features[i].present)         printf(" ... , we've got: %s\n", features[i].name);

you'll have check #if have_foo instead of #ifdef have_foo then, , --help message may displayed bit slower if number of features runs in zillions (in case i'd recommend different architecture anyway).


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