You should use the preprocessor macro __LINE__ and __FILE__. They are predefined macros and part of the C/C++ standard. During preprocessing, they are replaced respectively by a constant string holding an integer representing the current line number and by the current file name. Others preprocessor variables : __func__ : function name (this is part of … Read more
Yes. Pass gcc the -E option. This will output preprocessed source code.
Used properly, this can be a useful technique. Say you have a complex, performance critical subsystem with a fairly small public interface and a lot of non-reusable implementation code. The code runs to several thousand lines, a hundred or so private functions and quite a bit of private data. If you work with non-trivial embedded … Read more
Not only does it not get executed, it doesn’t even get compiled. #if is a preprocessor command, which gets evaluated before the actual compilation step. The code inside that block doesn’t appear in the compiled binary. It’s often used for temporarily removing segments of code with the intention of turning them back on later.
typedef obeys scoping rules just like variables, whereas define stays valid until the end of the compilation unit (or until a matching undef). Also, some things can be done with typedef that cannot be done with define. For example: typedef int* int_p1; int_p1 a, b, c; // a, b, c are all int pointers #define … Read more
A # on its own on a line has no effect at all. I assume it’s being used for aesthetic value. The C standard says: 6.10.7 Null directive Semantics A preprocessing directive of the form # new-line has no effect. The C++ standard says the same thing: 16.7 Null directive [cpp.null] A preprocessing directive of … Read more
I’d suggest using (unix util)xxd for this. you can use it like so $ echo hello world > a $ xxd -i a outputs: unsigned char a[] = { 0x68, 0x65, 0x6c, 0x6c, 0x6f, 0x20, 0x77, 0x6f, 0x72, 0x6c, 0x64, 0x0a }; unsigned int a_len = 12;
There is an argument counting trick that you can use. Here is one standard-compliant way to implement the second BAR() example in jwd’s question: #include <stdio.h> #define BAR(…) printf(FIRST(__VA_ARGS__) “\n” REST(__VA_ARGS__)) /* expands to the first argument */ #define FIRST(…) FIRST_HELPER(__VA_ARGS__, throwaway) #define FIRST_HELPER(first, …) first /* * if there’s only one argument, expands to … Read more
If they’re both strings you can just do: #define STR3 STR1 STR2 This then expands to: #define STR3 “s” “1” and in the C language, separating two strings with space as in “s” “1” is exactly equivalent to having a single string “s1”.
Standard C Preprocessor $ cat xx.c #define VARIABLE 3 #define PASTER(x,y) x ## _ ## y #define EVALUATOR(x,y) PASTER(x,y) #define NAME(fun) EVALUATOR(fun, VARIABLE) extern void NAME(mine)(char *x); $ gcc -E xx.c # 1 “xx.c” # 1 “<built-in>” # 1 “<command-line>” # 1 “xx.c” extern void mine_3(char *x); $ Two levels of indirection In a comment … Read more