3 ms·
One other thing that would be great that sometimes people use the preprocessor for is having the names variables/enums as runtime strings. Like, if you have an
by OskarS 5y ago
One other thing that would be great that sometimes people use the preprocessor for is having the names variables/enums as runtime strings. Like, if you have an enum and a function to get the string representation for debug purposes (i.e. the name of the enum as represented inside the source code):
typedef enum { ONE, TWO, THREE } my_enum;
const char* getEnumName(my_enum val);
you can use various preprocessor tricks to implement getEnumName such that you don't have to change it when adding more cases to the enum. This would be much better implemented with some compiler intrinsic/operator like `nameof(val)` that returned a string. C# does something similar with its `nameof`.
- Someone 5y ago> you can use various preprocessor tricks to implement getEnumName such that you don't have to change it when adding more cases to the enum. For those who don’t know: the X Macro (https://en.wikipedia.org/wiki/X_Macro https://en.wikipedia.org/wiki/X_Macro, https://digitalmars.com/articles/b51.html https://digitalmars.com/articles/b51.html)
- OskarS 5y agoHey, even an article written by Walter, that's a fun coincidence! :) This is slightly different than the form I've seen it, but same idea: in the version I've seen, you have a special file that's like "enums.txt" with contents like (warning, not tested): X(red) X(green) X(blue) and then you write: typedef enum { #define X(x) x #include "enums.txt" #undef X } color; const char* getColorName(color c) { switch (c) { #define X(x) case x: return #x; #include "enums.txt" #undef X } } Same idea, just using an #include instead of listing them in a macro. Thinking about it, it's sort-of a compile time "visitor pattern".
- WalterBright 5y agoAs an update, I removed all use of the X macro in my own code.
- Koshkin 5y agoI like that ONE == 0.
- OskarS 5y agoDid not even think about that :) Just so used to thinking of enums like that as opaque values.