This is awesome, I am going to divide by linux in my code everywhere in an attempt to obfuscate what I am doing.
At least anyone trying to port your code to Windows will be a bit surprised... :-)
Edit: Or /.*BSD/. :-(
Why does the C preprocessor interpret the word “linux” as the constant “1”?
11–20 of 60 posts
Re: Why does the C preprocessor interpret the word “linux” as the constant “1”?
#12Re: Why does the C preprocessor interpret the word “linux” as the constant “1”?
#13And that's why, in my opinion, non capitalized macros are always evil (yes, I'm looking at you linux kernel).
When I see a lowercase symbol used as a variable, I expect it's going to be some actual global variable. When I see a lower case symbol used like a function I expect it's an actual function. And then comes the day I want to take the address of the "function" and it fails. Or worse, I make a syntax error somewhere and because of the macro expansion it gives me the most perplexing error message in the world and it takes me 5 minutes and digging through 4 levels of include files to realize I forgot a colon or something.
Not to mention the mess if the macro is poorly implemented and does things like using a parameter several times which causes hard to catch undefined behaviours in the application. Nothing worse than having a seemingly harmless code like "foo(a++)" turn into the bug of doom because you didn't know foo was a macro. Please don't do that.
On the other end when I get a weird behaviour/error message around a capitalized symbol I automatically think that it must be a macro and go dig for the definition.
Re: Why does the C preprocessor interpret the word “linux” as the constant “1”?
#14Just a note: This was on the stackoverflow weekly newsletter yesterday. If you're interested in more questions like this it's worth to check it out, I like it a lot.
For anyone wondering where to subscribe: http://stackexchange.com/newsletters
PS: That's one of the few reddit customs I really like "link for the lazy" :)
Re: Why does the C preprocessor interpret the word “linux” as the constant “1”?
#15I spent at least an hour a while ago trying to track down a bug that turned out to be caused by exactly this. I couldn't work out what was happening until I looked at the preprocessor output.
I'm increasingly turning to -E to debug these hard-to-understand problems. I'd love a -E2 or what-have-you that would be even more verbose, and list all preprocess transformations applied to a line and the source lines where they were defined.
Unfortunately, the standard preprocessor output doesn't provide a convenient way to do this without a comment format. I guess you could use a do-nothing #pragma.
Eventually, I'm sure somebody will spin up some extension to clang to show you the complete evolution of a block of code and what other code contributed to that evolution.
Re: Why does the C preprocessor interpret the word “linux” as the constant “1”?
#16Wow. This would've been amazing news... back in in 1992.
Re: Why does the C preprocessor interpret the word “linux” as the constant “1”?
#17I spent at least an hour a while ago trying to track down a bug that turned out to be caused by exactly this. I couldn't work out what was happening until I looked at the preprocessor output.
I'm increasingly turning to -E to debug these hard-to-understand problems. I'd love a -E2 or what-have-you that would be even more verbose, and list all preprocess transformations applied to a line and the source lines where they were defined. Unfortunately, the standard preprocessor output doesn't provide a convenient way to do this without a comment format. I guess you could use a do-nothing #pragma. Eventually, I'…
Emacs has a "c-macro-expand" function which is quite hackish but extremely useful, IMO: it attempts to macro expand the region.
For instance running it on the following code in the middle of a C source file:
#define BOGO_MAX(a, b) a > b ? a : b
int test()
{
return BOGO_MAX(3 + 4, 5);
}
int test()
{
return 3 + 4 > 5 ? 3 + 4: 5;
}Re: Why does the C preprocessor interpret the word “linux” as the constant “1”?
#18Linux is No. 1
Re: Why does the C preprocessor interpret the word “linux” as the constant “1”?
#19Earlier quoted context omitted.
I'm increasingly turning to -E to debug these hard-to-understand problems. I'd love a -E2 or what-have-you that would be even more verbose, and list all preprocess transformations applied to a line and the source lines where they were defined. Unfortunately, the standard preprocessor output doesn't provide a convenient way to do this without a comment format. I guess you could use a do-nothing #pragma. Eventually, I'…
Emacs has a "c-macro-expand" function which is quite hackish but extremely useful, IMO: it attempts to macro expand the region. For instance running it on the following code in the middle of a C source file: #define BOGO_MAX(a, b) a > b ? a : b int test() { return BOGO_MAX(3 + 4, 5); } Creates a new buffer containing: int test() { return 3 + 4 > 5 ? 3 + 4: 5; }
How well does that play with ifdef? The problem is rarely what does this macro expand to, but which macro is going to be expanded.
Re: Why does the C preprocessor interpret the word “linux” as the constant “1”?
#20Earlier quoted context omitted.
Emacs has a "c-macro-expand" function which is quite hackish but extremely useful, IMO: it attempts to macro expand the region. For instance running it on the following code in the middle of a C source file: #define BOGO_MAX(a, b) a > b ? a : b int test() { return BOGO_MAX(3 + 4, 5); } Creates a new buffer containing: int test() { return 3 + 4 > 5 ? 3 + 4: 5; }
How well does that play with ifdef? The problem is rarely what does this macro expand to, but which macro is going to be expanded.
Well, I guess it depends on what your code looks like.
That being said if I'm not sure if some code is being compiled I just add an "#error foo" and rebuild. Or even simpler I just type in some garbage to trigger a compilation error.