Question

I have a system where I specify on the command line the verbosity level. In my functions I check against what was specified to determine if I enter a code block or not:

#ifdef DEBUG
if (verbose_get_bit(verbose_level_1)) {
    // arbitrary debugging/printing style code generally goes in here, e.g.:
    printf("I am printing this because it was specified and I am compiling debug build\n");
}
#endif

I’d like to make this less tedious to set up, so here’s what I have so far:

// from "Verbose.h"
bool verbose_get_bit(verbose_group_name name); // verbose_group_name is an enum
#ifdef DEBUG
#define IF_VERBOSE_BIT_D(x) if (verbose_get_bit(x))
#else // not debug: desired behavior is the entire block that follows gets optimized out
#define IF_VERBOSE_BIT_D(x) if (0)
#endif // not debug

Now, I can do this:

IF_VERBOSE_BIT_D(verbose_GL_debug) {
    printf("I don't want the release build to execute any of this code");
    glBegin(GL_LINES);
    // ... and so on
}

I like this because it looks like an if-statement, it functions as an if-statement, it’s clear that it’s a macro, and it does not get run in the release build.

I’d be reasonably sure that the code will get optimized out since it will be wrapped in a if(false) block but I would prefer it if there was some way I can get the preprocessor to actually throw the entire block away. Can it be done?

Answer 1

I can’t think of a way to do it without wrapping the entire block in a macro.

But this might work for your purposes:

#if DEBUG
#define IF_VERBOSE_BIT_D(x) {x}
#else
#define IF_VERBOSE_BIT_D(x)
#endif

IF_VERBOSE_BIT_D(
    cout << "this is" << endl;
    cout << "in verbose" << endl;
    printf("Code = %d\n", 1);
)

Indeed the compiler should be able to optimize out an if (0), but I often do something similar to this when the code inside the block will not compile at all when not in debug mode.