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. What is define ( [ , function ]) in javascript The #define directive is a preprocessor directive
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The preprocessor replaces those macros by their body before the compiler even sees it
Think of it as an automatic search and replace of your source code
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 #define width 10 is a preprocessor directive that allows you to specify a name (width) and its replacement text (10) The preprocessor parses the source file and each occurrence of the name is replaced by its associated text
The compiler never actually sees a macro name at all, what it sees is the replaced text. #define simply substitutes a name with its value 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.
As far as i know, what you're trying to do (use if statement and then return a value from a macro) isn't possible in iso c.but it is somewhat possible with statement expressions (gnu extension)
I've found that this works on gcc and clang by default: 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. 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? I want to use the pi constant and trigonometric functions in some c++ program I get the trigonometric functions with include <math.h> However, there doesn't seem to be a definition for pi i.
