This create a macro named EPOLLIN whose replacement text is also EPOLLIN. This is most likely a way for the preprocessor to check which event codes are available and conditionally compile code as necessary. If we go to the git repo for glibc and look at the output of git blame we see the following … Read more
As for the updated question, by the use of auxiliary macro VA_ARGS like the following, the arguments will be expanded as expected. #define VA_ARGS(…) , ##__VA_ARGS__ #define CALL(f,…) FN(f)->call((ref(new LinkedList()) VA_ARGS(__VA_ARGS__)))
Project properties -> C/C++ -> Preprocessing -> Preprocess to a file: Yes (/P) The files will be called .i and will be created in the build directory. Also see the msdn page.
Integer arithmetic? Run the following program to find out: #include “stdio.h” int main() { #if 1 + 1 == 2 printf(“1+1==2\n”); #endif #if 1 + 1 == 3 printf(“1+1==3\n”); #endif } The answer is “yes”. There is a way to make the preprocessor perform integer arithmetic, which is to use it in a preprocessor condition. … Read more
On the introduction page of Boost.Preprocessor, an example is given in A.4.1.1 Horizontal Repetition #define TINY_print(z, n, data) data #define TINY_size(z, n, unused) \ template <BOOST_PP_ENUM_PARAMS(n, class T)> \ struct tiny_size< \ BOOST_PP_ENUM_PARAMS(n,T) \ BOOST_PP_COMMA_IF(n) \ BOOST_PP_ENUM( \ BOOST_PP_SUB(TINY_MAX_SIZE,n), TINY_print, none) \ > \ : mpl::int_<n> {}; BOOST_PP_REPEAT(TINY_MAX_SIZE, TINY_size, ~) // Oh! a tilde! #undef … Read more
Inspired by chris’s answer.1 #define PP_THIRD_ARG(a,b,c,…) c #define VA_OPT_SUPPORTED_I(…) PP_THIRD_ARG(__VA_OPT__(,),true,false,) #define VA_OPT_SUPPORTED VA_OPT_SUPPORTED_I(?) If __VA_OPT__ is supported, VA_OPT_SUPPORTED_I(?) expands to PP_THIRD_ARG(,,true,false,), so the third argument is true; otherwise, VA_OPT_SUPPORTED_I(?) expands to PP_THIRD_ARG(__VA_OPT__(,),true,false,), the third argument is false. Edit: As Edward Diener’s answer notes, GCC >= 8 issues a warning or error whenever it sees __VA_OPT__, … Read more
[Edit: I assume you want to use compile-time macros to determine which environment you’re on. Maybe you want to determine if you’re running on Wine under Linux or something instead of Windows, but in general, your compiler targets a specific environment, and that is either Windows (DOS) or it isn’t, but it’s rarely (never?) both.] … Read more
It tells the compiler where the following line actually came from. It’s usually only the C preprocessor that adds these, for example, when including a file, it tells the compiler (which is basically only seeing one stream of data) that we’re looking at a different file. This may sound strange, but the preprocessor simply inserts … Read more
For adding quotes you need this trick: #define Q(x) #x #define QUOTE(x) Q(x) #ifdef FILE_ARG #include QUOTE(FILE_ARG) #endif
The GHC documentation has a section relating to the C pre-processor that documents some of the predefined pre-processor macros. The Cabal documentation has a section relating to conditional compilation that gives an example relating to base. If you are writing a portable package, you should be using Cabal, anyway.