[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
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.
What you are asking for is possible but needs a bit of work. Define a preprocessor variable in your csproj <PropertyGroup Condition=” ‘$(OS)’ == ‘Windows_NT’ “> <DefineConstants>_WINDOWS</DefineConstants> </PropertyGroup> Use that in your code #if _WINDOWS // your windows stuff #else // your *nix stuff #endif I find this technique useful when you have constants that … 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
Why not use the standard library? #include <bitset> int bits_in(std::uint64_t u) { auto bs = std::bitset<64>(u); return bs.count(); } resulting assembler (Compiled with -O2 -march=native): bits_in(unsigned long): xor eax, eax popcnt rax, rdi ret It is worth mentioning at this point that not all x86 processors have this instruction so (at least with gcc) you … Read more
I’ve created one today, and tested on GCC4.6.0. #include <iostream> #define E(L,I) \ (I < sizeof(L)) ? L[I] : 0 #define STR(X, L) \ typename Expand<X, \ cstring<E(L,0),E(L,1),E(L,2),E(L,3),E(L,4), E(L,5), \ E(L,6),E(L,7),E(L,8),E(L,9),E(L,10), E(L,11), \ E(L,12),E(L,13),E(L,14),E(L,15),E(L,16), E(L,17)> \ cstring<>, sizeof L-1>::type #define CSTR(L) STR(cstring, L) template<char …C> struct cstring { }; template<template<char…> class P, typename S, typename … 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
This is the process: source header source header header \ / \ | / / \ / \ | / / PREPROCESSOR PREPROCESSOR | | V V preprocessed code preprocessed code | | COMPILER COMPILER | | V V object code object code \ / \ / \ / LINKER | V executable Preprocessing #include … Read more
You can do something like this in a header file: // // generic.h // #define TOKENPASTE(x, y) x ## y #define GET_MINIMUM(T) TOKENPASTE(get_minimum_, T) TYPE GET_MINIMUM (TYPE) (TYPE * nums, size_t len){ TYPE min = nums[0]; for (size_t i = 1; i < len; i++) { if (nums[i] < min) { min = nums[i]; } … Read more
You can choose the “Show the Assistant editor” view in the top right set of buttons in the toolbar. Then, at the top of the right-hand editor you can click the little Related Files button and then either choose Preprocess or Assembly. You can see an example of both the preprocessor output and generated assembly … Read more