c-preprocessor

I am trying to execute the following code: #define channel1 10 #define channel(id) channel##id int main(){ int id = 1; cout << channel(id)<<"\n"; return 0; } I get the following error: error: use of undeclared identifier 'channelid' Instead, I want an output to be 10 , as channel(id) should be preprocessed to channel1 and which replaces the value with 10. Is there any way to achieve it? The problem is caused because you're trying to mix information that it is considered at different stages in the processing of the code. Macros and all CPP (C-Pre-Processor) stuff happens (as its own name

I came across a piece of code where NULL is typecast to an structure pointer type (foo *) 0 , and with that pointer de-referencing a member ((foo *)0)->m , and using address of that &(((foo *)0)->m)) and type casting it to integer to get the memory index of that member with in the structure. ((unsigned int)(&(((foo *)0)->m))) . To my knowledge NULL pointer dereference should always result a segmentation fault in C. But I don't understand how NULL pointer can be de-referenced like this and still not result in a segmentation fault. #include <stdio.h> #define MACRO(m) ((unsigned int)(&(((foo *)0)

Im interested to add in some extra logic around existing function calls, by wrapping them without renaming them. (just for a test) . The existing solutions I found rely on wrapping a function in a macro of a different name, which can mean changing a lot of code. Any suggestions? Note, I'm aware of LD_PRELOAD , but am interested to use macro's to be able to inspect the arguments passed to the function (using _Generic for example). There's normally no need to rename macro-wrapped functions because inside the expansion of a macro, the macro's name is not expanded. Here's an example straight from

I have a project in C++ that I would like to view the preprocessor output to see what some #defines and macros would look like. I tried the /p switch to turn on the preprocess to a file option to the compiler (it turns off full compilation and only runs the preprocessor) but my project now refuses to compile and shows a long list of errors starting with: "Cannot open include file: 'stdafx.h': No such file or directory". The project compiles fine without the /p argument, of course. Any suggestions? If you run cl.exe on its own then you would need to supply all the same parameters as the IDE

Is there a standard definition for the size of the __DATE__ and __TIME__ strings in ANSI C? The motivation behind this question is: I have two applications running on two different CPUs. During runtime, app #1 receives date and time (as part of version-info) from app #2. Of course, app #2 takes them from the preprocessor __DATE__ and __TIME__ definitions. So I would like to know whether or not I can statically allocate in app #1 an array, into which I can copy the info received from app #2. Thanks Vignesh Kumar A __DATE__ The date of translation of the source file (a character string literal

Using a #define while initializing an array #include <stdio.h> #define TEST 1; int main(int argc, const char *argv[]) { int array[] = { TEST }; printf("%d\n", array[0]); return 0; } compiler complains: test.c: In function ‘main’: test.c:7: error: expected ‘}’ before ‘;’ token make: *** [test] Error 1 Using a #define as functional input arguments #include <stdio.h> #define TEST 1; void print_arg(int arg) { printf("%d", arg); } int main(int argc, const char *argv[]) { print_arg(TEST); return 0; } compiler complains: test.c: In function ‘main’: test.c:12: error: expected ‘)’ before ‘;’ token make