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
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’t expand macros in strings, but you can write #define COLOR “#00ff00” f(“abc “COLOR); Remember that this concatenation is done by the C preprocessor, and is only a feature to concatenate plain strings, not variables or so.
NOTE: To be extra clear, you DO NOT need to wrap your preview providers in #if DEBUG conditionals. They are removed from your production build. I’m a little late, but I just had to make note of this because the confusion is all over the web and it turns out to be quite comical. The … Read more
A little bit confused still. What will the result be without ##? Usually you won’t notice any difference. But there is a difference. Suppose that Something is of type: struct X { int x; }; X Something; And look at: int X::*p = &X::x; ANALYZE(x, flag) ANALYZE(*p, flag) Without token concatenation operator ##, it expands … 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
Pre-processor macros perform text-replacement before the code is compiled so SQR(b+5) translates to (b+5*b+5) = (6b+5) = 6*3+5 = 23 Regular function calls would calculate the value of the parameter (b+3) before passing it to the function, but since a macro is pre-compiled replacement, the algebraic order of operations becomes very important.
So like the others say, no, you can’t have #include statements inside a macro, since the preprocessor only does one pass. However, you can make the preprocessor do basically the same thing with a gnarly trick I found myself using recently. Realise that preprocessor directives won’t do anything inside a macro, however they WILL do … Read more