Define

Understanding define requires examining multiple perspectives and considerations. c++ - What does ## in a #define mean? In other words, when the compiler starts building your code, no #define statements or anything like that is left. A good way to understand what the preprocessor does to your code is to get hold of the preprocessed output and look at it. What is the scope of a #define? I have a question regarding the scope of a #define for C/C++ and am trying to bet understand the preprocessor.

Let's say I have a project containing multiple sour... Another key aspect involves, c preprocessor - Is there a good reason for always enclosing a define .... #define _add_penguin(a) penguin ## a #define add_penguin(a) _add_penguin(a) #define WIDTH (100) #define HEIGHT 200 add_penguin(HEIGHT) // expands to penguin200 add_penguin(WIDTH) // error, cannot concatenate penguin and (100) Same for stringization (#). Clearly this is a corner case and probably doesn't matter considering how WIDTH will presumably be used.

Still, it is something to keep in ... Additionally, is it possible to use a if statement inside #define?. 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... Building on this, but it is somewhat possible with statement expressions (GNU extension). Since #define s are essentially just fancy text find-and-replace, you have to be really careful about how they're expanded. I've found that this works on gcc and clang by default:

c# - How do you use #define? 8 #define is used to define compile-time constants that you can use with #if to include or exclude bits of code. How do I show the value of a #define at compile-time?.

I know that this is a long time after the original query, but this may still be useful. This can be done in GCC using the stringify operator "#", but it requires two additional stages to be defined first. #define XSTR(x) STR(x) #define STR(x) #x The value of a macro can then be displayed with: #pragma message "The value of ABC: " XSTR(ABC) See: 3.4 Stringification in the gcc online ...

c++ - Declaring a function using #define - Stack Overflow. 2 #define is part of something called the "preprocessor." Essentially, this is the code that is processed before the C document is compiled. Most of the preprocessor code is in a file with a ".h" extension (which is why you may have seen that when importing libraries). The preprocessor language is primitive. c - How do I concatenate #define value?

You'll need to complete a few actions and gain 15 reputation points before being able to upvote. Upvoting indicates when questions and answers are useful. Another key aspect involves, what's reputation and how do I get it? Instead, you can save this post to reference later.