Lazy evaluation makes macros redundant This is pure nonsense (not your fault; I’ve heard it before). It’s true that you can use macros to change the order, context, etc. of expression evaluation, but that’s the most basic use of macros, and it’s really not convenient to simulate a lazy language using ad-hoc macros instead of … Read more
That’s a really good question. I think it’s nuanced but definitely answerable: Macros are not stuck in s-expressions. See the LOOP macro for a very complex language written using keywords (symbols). So, while you may start and end the loop with parentheses, inside it has its own syntax. Example: (loop for x from 0 below … Read more
. separates tokens and so you can’t use ## as .red is not a valid token. You would only use ## if you were concatenating two tokens into a single one. This works: #define X(a, b) foo.a = -1; What’s a valid proprocessing token? Can someone explain this? It is what gets parsed/lexed. foo.bar would … Read more
If you can use a C++ compiler to build the object file that you want to contain your version string, then we can do exactly what you want! The only magic here is that C++ allows you to use expressions to statically initialize an array, while C doesn’t. The expressions need to be fully computable … Read more
from the C# faq. http://blogs.msdn.com/CSharpFAQ/archive/2004/03/09/86979.aspx Why doesn’t C# support #define macros? In C++, I can define a macro such as: #define PRODUCT(x, y, z) x * y * z and then use it in code: int a = PRODUCT(3, 2, 1); C# doesn’t allow you to do this. Why? There are a few reasons why. … Read more
The value for C++20 is 202002L, as you can see at [cpp.predefined]p1.1: __cplusplus The integer literal 202002L. [ Note: It is intended that future versions of this International Standard will replace the value of this macro with a greater value. — end note ] Therefore, for compilers that already implement the new standard, you can … Read more
tl;dr: For C++17, __cplusplus is 201703L. What is the value of __cplusplus when using C++17? According to the draft standard N4594 §16.8/p1 Predefined macro names [cpp.predefined] (Emphasis Mine): The following macro names shall be defined by the implementation: __cplusplus The name __cplusplus is defined to the value 201402L when compiling a C++ translation unit.156 156) … Read more
You can but you shouldn’t. The shouldn’t part: You shouldn’t because using the pre-processor in that way is considered bad practice to start with, and there are better and more Java-idiomatic ways to solve this use case. The can part: (*) Java itself doesn’t support macros. On the other hand, you could pipe the source … Read more
In this context (applied to a parameter reference in a macro definition), the pound sign means to expand this parameter to the literal text of the argument that was passed to the macro. In this case, if you call PRINT(5) the macro expansion will be printf(“5” “%d\n”, 5); which will print 5 5; not very … Read more
Imagine you wrote this: #define Max(a,b) (a < b ? b : a) int x(){ turnLeft(); return 0; } int y(){ turnRight(); return 1; } then called it like this: auto var = Max(x(), y()); Do you know that turnRight() will be executed twice? That macro, Max will expand to: auto var = (x() < … Read more