c-preprocessor

In Xcode 6.1.1 (Obj-C) #if 1 NSLog(@"print 1"); #endif #if TRUE NSLog(@"print TRUE"); #endif #if YES NSLog(@"print YES"); #endif And the result: print 1 print TRUE Can explain to me the result ? Why #if TRUE vs #if YES vs #if 1 are different? Mhm... I`m not really an objective-c person, I personally like c++ better, but let me try to answer you anyways. if 1 The compiler, in the end of it, like pretty much everything in computers, runs on zeros and ones. When you write an "if 1" statement in your code, it will always do it, like every other number you might put there - that is, except zero.

I've got some code that can run with (or without) OpenMP - it depends on how the user sets up the makefile. If they want to run with OpenMP, then they just add -fopenmp to CFLAGS and CXXFLAGS . I'm trying to determine what preprocessor macro I can use to tell when -fopenmp is in effect. The omp.h header does not look very interesting: $ cat /usr/lib/gcc/x86_64-linux-gnu/4.8/include/omp.h | grep define #define OMP_H 1 #define _LIBGOMP_OMP_LOCK_DEFINED 1 # define __GOMP_NOTHROW throw () # define __GOMP_NOTHROW __attribute__((__nothrow__)) And I can't get the preprocessor to offer up anything

I use #include ".../frontend/tokens.mll" in lexer.mll , and then cpp -C -P frontend/lexer.mll -o frontend/lexer_new.mll to generate lexer_new.mll . That worked until I upgraded my ubuntu from 12.04 to 14.04 yesterday. The compilation gives an error: ocamllex frontend/lexer_new.mll File "frontend/lexer_new.mll", line 1, character 1: illegal character /. make: *** [frontend/lexer_new.ml] Error 3 That is because in lexer_new.mll several lines of C comments have been inserted in the beginning: /* Copyright (C) 1991-2014 Free Software Foundation, Inc. This file is part of the GNU C Library. The GNU

I have a lot of functions to declare in this format: int foo_100(int, int); int foo_200(int, int); int foo_300(int, int); int foo_400(int, int); typedef int (*foo)(int, int); struct foo foo_library[] = { foo_100, foo_200, foo_300, foo_400 }; Is there a way I can use the C preprocessor to partially automate this task? Ideally, something like this: foo.txt 100 200 300 400 foo.h typedef int (*foo)(int, int); #define DEFINE_FOO(id_) int foo_##id_(int, int); DEFINE_FOO(#include"foo.txt") struct foo foo_library[] = { #include "foo.txt" }; You could use the X macro trick: // foo_list.h #define MY

I have been thinking about how macros can be written to be safe, readable and intuitive. Proper use of them should be understood by the looks of them and when used incorrectly the compiler should tell you, and not let you introduce an obscure bug. When writing multiple line define macros I usually find myself constructing them like this to fullfill the desired criteria: #define macro(x) do{ \ ... some code line ; \ ... some code line ; \ }while(0) This way you can both... if (a) { macro(a); } and... if (a) macro(a); else { ... } A nice feature of this is that if you use them incorrectly you

I was thinking it would be nice to set up my global GHCI config such that my commonly-used imports occur automatically when the packages that provide them are present. I tried adding this to ~/.ghc/ghci.conf : :set -XCPP #ifdef MIN_VERSION_containers import Data.Set (Set) import qualified Data.Set as Set import Data.Map (Map) import qualified Data.Map as Map #endif But apparently that does not work. > stack repl Configuring GHCi with the following packages: GHCi, version 8.0.2: http://www.haskell.org/ghc/ :? for help <interactive>:24:1: error: parse error on input ‘#’ <interactive>:29:1: error