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POC debugging macro (with different debug "sources")
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  1. POC debugging macro (with different debug "sources")
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    copied!<p>I set out to get myself a neat C debugging macro, not really sure what I really wanted (and being clueless when it comes to macros) I turned to google. Some time later and I now think I know what I want, but not how it works. I haven't had much luck with getting decent information about macros and techniques for debugging.</p> <p>What I've been using in the past have been something like this:</p> <pre><code>#ifdef DEBUG #define DBG(x) printf x #else #define DBG(x) /* nothing */ #endif </code></pre> <p>Problem is that it can get quite messy and ultimately you end up commenting out old debug messages eventhough you probably will need them later on.</p> <p>The best example I found was from some slides from an advanced c course, which can be found here: <a href="http://www.mpi-inf.mpg.de/departments/rg1/teaching/advancedc-ws08/script/lecture07.pdf" rel="nofollow noreferrer">http://www.mpi-inf.mpg.de/departments/rg1/teaching/advancedc-ws08/script/lecture07.pdf</a> (the relevant parts are slide 19-23, but most of it is included below)</p> <p>Being lecture slides they unfortunately need some explaining to go. But they mention something that seems quite useful:</p> <pre><code>DBG((MOD_PARSER , "z = %d\n", z)); </code></pre> <p>Where MOD_PARSER is a debug module/category and the rest of the arguments are meant to be given to printf.</p> <p>And the implementation of DBG:</p> <pre><code>#ifdef PRGDEBUG #define DBG(x) dbg_printer x #else #define DBG(x) /* nothing */ #endif void dbg_printer(int module , const char *fmt, ...); </code></pre> <p>Problem #1 is to write the dbg_printer function, I'm not sure how to pass the variable number of arguments to an printf statement.</p> <p>The slides go on to discuss how to elegantly add new modules and I'm fairly certain that I haven't understood this at all, but anyway...</p> <pre><code>*How to add new modules elegantly *Add a file debug_modules.def ADD_MOD(0, PARSER) ADD_MOD(1, SOLVER) ADD_MOD(2, PRINTER) </code></pre> <p>...</p> <pre><code>*“Generate” an enum with debug modules: debug.h ... #define ADD_MOD(num, id) MOD_ ## id = 1 &lt;&lt; num, enum _debug_modules_t { #include "debug_modules.def" }; #undef ADD_MOD ... </code></pre> <p>...</p> <pre><code>*Preprocessor yields enum _debug_modules_t { MOD_PARSER = 1 &lt;&lt; 0, MOD_SOLVER = 1 &lt;&lt; 1, MOD_PRINTER = 1 &lt;&lt; 2, }; </code></pre> <p>I don't see why you would left-shift the values of the enumeration elements, some nifty trick I'm missing? </p> <p>Aside from the slides above I haven't seen a single example or article/post/whatever even mentioning this so maybe this isn't even suitable for my purposes. Does this sound reasonable and are similar techniques actually used?</p> <p>As of now the question is how to implement dbg_printer and really how the debug modules enumeration is supposed to work, but seeing as how I might have misunderstood everything that might change :(</p>
 

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