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[C question] Best way to change features of the program at compile time: #if((n)def) or if (const)? (kbin.social)

submitted 1 year ago* (last edited 1 year ago) by mkulko@kbin.social to c/programming@kbin.social

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Suppose that I have two features in my C program, feature foo and feature bar. I wish to be able to switch what features will be compiled into my program at compile time. The only two ways I know of doing this are:

Using preprocessor directives

#define MYPROG_FEATURE_FOO 1
#define MYPROG_FEATURE_BAR 1

/* ... */

#if MYPROG_FEATURE_FOO == 1
/* code related to feature foo */
#else
/* code to prompt people to pay for the absolutely proprietary version of my program */
#endif

/* ... */

#if MYPROG_FEATURE_BAR == 1
/* code related to feature bar */
#else
/* code to prompt people to pay for the absolutely proprietary version of my program */
#endif

/* ... */

Using the normal if with a const, non-volatile variable

const _Bool myprog_feature_foo = 1;
const _Bool myprog_feature_bar = 1;

/* ... */

if (myprog_feature_foo)
{
  /* code related to feature foo */
}
else
{
  /* buy proprietary version or no feature for you >:) */
}

/* ... */

if (myprog_feature_bar)
{
  /* code related to feature bar */
}
else
{
  /* buy proprietary version or no feature for you >:) */
}

/* ... */

What's the better way to do this? Is there a third way to achieve this that I have missed that's better than the above two?

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[–] alejandro@kbin.social 4 points 1 year ago

Another way would be to keep the proprietary code in their own compilation units, and replace them with a dummy/stub implementation from your build system at config time (e.g. CMake option + if() statement). One benefit to this is that you don't have to litter your codebase with a bunch of preprocessor directives.

There's no "better" way though, just pick the one you find easier to manage.