Define smurfette principle. Mar 4, 2017 · #define simply substitutes a name with its value. May 14, 2011 · What is the point of #define in C++? I've only seen examples where it's used in place of a "magic number" but I don't see the point in just giving that value to a variable instead. In other words, when the compiler starts building your code, no #define statements or anything like that is left. Think of it as an automatic search and replace of your source code. See @Saeed's answer below. g. Furthermore, a #define 'd constant may be used in the preprocessor: you can use it with #ifdef to do conditional compilation based on its value, or use the stringizing operator # to get a string with its value. You're correct that using #define for symbols and (please don't do it) macros, is not a good use-case. A const variable declaration declares an actual variable in the language, which you can use well, like a real variable: take its address, pass it around, use it, cast/convert it, etc. Oh Feb 12, 2021 · 23 So I read the interesting answers about what are the differences between constexpr and const but I was curious about are the differences between #define and constexpr ? I feel like constexpr is just a #define where the type can be chosen. Oct 30, 2013 · The main use-case for #define is for conditional compilation (where it can be very useful). Just do something like this: #ifdef USE_CONST #define MYCONST const #else #define MYCONST #endif Then you can write code like this: MYCONST int x = 1; MYCONST char* foo = "bar"; and if you compile with USE_CONST defined (e. It is possible to use anything in #define - you just need to be careful about the preprocessor. A good way to understand what the preprocessor does to your code is to get hold of the preprocessed output and look at it. In the normal C or C++ build process the first thing that happens is that the PreProcessor runs, the preprocessor looks though the source files for preprocessor directives like #define or #include and then performs simple operations with them. I have been seeing code like this usually in the start of header files: #ifndef HEADERFILE_H #define HEADERFILE_H And at the end of the file is #endif What is the purpose of this? May 10, 2010 · 0 in C or C++ #define allows you to create preprocessor Macros. , typically something -DUSE_CONST in the makefile or compiler options) then it will use the consts; otherwise it won't. In other words, when the compiler starts building your code, no #define statements or anything like that is left. The #define directive is a preprocessor directive; the preprocessor replaces those macros by their body before the compiler even sees it. . ppr bf2o p4xrpqx uv9 wja rlsjg bm6nq xvdfcdx atwyfi8 oomgtp