#define TOPLEFT 0x01;
#define TOPRIGHT 0x02;
#define RIGHTTOP 0x04;
#define RIGHTBOTTOM 0x08;
#define BOTTOMRIGHT 0x10;
#define BOTTOMLEFT 0x20;
#define LEFTBOTTOM 0x40;
#define LEFTTOP 0x80;
int main()
{
char a = 0x40 | 0x80; // <--- this is OK
char b = LEFTBOTTOM | LEFTTOP; // E2188: expression syntax error
return 0;
}
Preprocessor failure?
Author
Hello,
I've got a kind of weird (to me, its weird) problem.
I define a few words and then want to use them.
So to combine the LEFTBOTTOM with the LEFTTOP I use a bitwise or, | .
The problem is, the preprocessor doesn't do, what it is supposed to do. (or isn't doing what I think it should be doing ;) )
I think this small program will make it clear:
If the precessor replaces all the defines, it is exactly the same as char a = 0x40 | 0x80 (the previous line) and should not throw me an error.
Any help is appreciated.
Thanks in advance.
Kamos
#define directives don't end with a semicolon. Guess where those semicolons are ending up? [smile]
You'd probably be better off using const variables instead of #define macros. It gets around the invisible preprocessor (invisible in that the compiler doesn't catch errors until after the preprocessor does its work).
Author
Ah ofcourse!
And yes I guess const variables would be better, but it introduces a lot of work...
Say I'd use a const variable. When I use 2 classes, which make use of these const variables, I will have to declare these const variables twice. (once in each class).
This is double work. (and gets worse when using more classes)
Or am I wrong?
The preprocessor allows me to define names and use the defined names anywhere I want. (with the side effect of invisible errors...)
And yes I guess const variables would be better, but it introduces a lot of work...
Say I'd use a const variable. When I use 2 classes, which make use of these const variables, I will have to declare these const variables twice. (once in each class).
This is double work. (and gets worse when using more classes)
Or am I wrong?
The preprocessor allows me to define names and use the defined names anywhere I want. (with the side effect of invisible errors...)
You can put const static int TOPLEFT = 0x01; in a header file (not in a class definition) and it'll be available anywhere that header file is included.
For that matter, an enumeration might be more appropriate to what you're doing.
For that matter, an enumeration might be more appropriate to what you're doing.
This topic is closed to new replies.
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