c-preprocessor

Please tell me the answer with explanation: #define f(g,h) g##h main(){ printf("%d",f(100,10)); } ## is used to concatenate whatever is before the ## with whatever is after it. It is used for concatenation. You can check the reference for details A ## operator between any two successive identifiers in the replacement-list runs parameter replacement on the two identifiers (which are not macro-expanded first) and then concatenates the result. This operation is called "concatenation" or "token pasting". 来源： https://stackoverflow.com/questions/29577775/what-does-mean-in-the-define-directive-in-the

#define SOUND_SPEED 0.034; int rtt; //round trip time in microsecond double distance; distance = (double)(rtt*SOUND_SPEED)/2; It complains error: expected expression before '/' token. Was is it bacause I can't use macro to define decimals or what? Drop the semicolon: #define SOUND_SPEED 0.034; ^ If you keep it the generated code will look like this: distance = (double)(rtt*SOUND_SPEED;)/2; ^ #define SOUND_SPEED 0.034; ^ Do not use the trailing ; Actually you should never terminate a macro with a ; : PRE11-C. Do not conclude macro definitions with a semicolon https://www.securecoding.cert.org

I have googled turning off the gcc preprocessor on linux for a good while now (using that exact phrase) and everything has been irrelevant. For example I want to turn off everything except the preprocessor (the opposite of what I want) or pressurising warnings. Does anyone know of a way to disable the preprocessor? I found one that Facebook developed and claimed is faster, and I would like to test it out. I tested what lornix said in a comment, and it works: Name the other/newer preprocessor "cpp" and put it in your path, and rename the original cpp to cpp-other or cpp-orig. It'll work great

Being faced with the question whether it's possible to choose #include s in the preprocessor I immediately thought not possible . .. Only to later find out that it is indeed possible and you only need to watch out for argument expansions (which e.g. Boost.Preprocessor can take care of). While I'd avoid actually doing that for includes if possible, I'd like to know why this works. At the moment I fail to get a useful understanding in the C++ or C standard. Are parameterized macros allowed for any preprocessor-directive? (except #define / #undef ) Can someone reference where this is allowed and

I'm using a proprietary development environment that compiles code written in C , as well as the IEC 61131 languages. For the C compilation, it uses GCC 4.1.2 with these build options: -fPIC -O0 -g -nostartfiles -Wall -trigraphs -fno-asm The compilation is done by a program running on windows utilizing Cygwin. My issue is, IEC language preprocessor is not that useful (doesn't support #define at all) and I want to use macros! I don't see why the GCC preprocessor would really care what language it is processing (my target language is Structured Text), so I'm looking to see if anyone might know a