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.
Is it possible to place a macro in a namespace in c++? No. #define is a preprocessor directive. The macros are being replaced before anything else apart from removing comments (which means, before compilation). So at the time macros are replaced, the compiler knows nothing about your namespaces. As other people state, in your case … Read more
From etc/NEWS: * Lisp Changes in Emacs 24.4 … ** New macro `with-eval-after-load’. This is like the old `eval-after-load’, but better behaved. Emacs 24.4 was released on 20th October 2014. eval-after-load is considered ill-behaved because it is a function, not a macro, and thus requires the code inside it to be quoted, which means that … 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.
It turns a block into a single statement. If you just use a block (i.e. code enclosed in {}) strange things can happen, for example #define STUFF() \ { do_something(); do_something_else(); } if (cond) STUFF(); else //… the extra semi-colon breaks the syntax. The do {} while(false) instead is a single statement. You can find … Read more
This behavior is underspecified but intended, though it might appear confusing. We plan to elaborate on the role of return type in macro signatures, but at the moment I feel like the flexibility is a good thing to have. Also at times the behavior is inconsistent, e.g. when the macro is caught in the middle … Read more
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
(std::min)(x,y) The parentheses around min prevent macro expansion. This works with all function macros.
It’s not exactly search and replace, it’s token expansion. C macros are what every other kind of macro is in the computing world: a way to write something short and simple and have it automatically turn into something longer and more complicated. One reason macros are used is performance. They are a way of eliminating … Read more
This article answers your question: C/C++ tip: How to detect the operating system type using compiler predefined macros (plus archive.org link in case it vanishes). The article is quite long, and includes tables that are hard to reproduce, but here’s the essence: You can detect Unix-style OS with: #if !defined(_WIN32) && (defined(__unix__) || defined(__unix) || … Read more