I can't think of a particular good example, but say you write a swap macroOriginally Posted by Dave_Sinkula
You will get a return value if you use parenthesis, namely the new value of x. (or is it?) That has to become handy in some situation, I know it!Code:#define SWAP_NUM(x, y) ( \ (x) += (y), \ (y) = (x)-(y), \ (x) -= (y) \ )
That's using the comma operator which performs each expression and the value of the last expression evaluated is used as the expression's value. That entire thing is an expression which therefore may be stuffed into (), if however you wanted a common statement like while (which probably is going to use {}) you can see you will get an error.
No, that isn't a particularly good example, since that is one of the forms of swapping to avoid. And no, you don't really "get a return value". Run it through the precompiler and see what madness you have actually written.
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That's bad! (i guess)But I am only trying to learn the language, what you can do and what you can't. Besides, how do you run the precompiler? I am currently using DevCpp.
And that kind of swap, is it bad because it does not leave the exact values when swaping float values? Consider the xor swap instead then.
Last edited by TriKri; 08-01-2006 at 07:42 AM.
To stop after preprocessing the file, pass -E to GCC at the command line or in the compiler arguments:how do you run the precompiler? I am currently using DevCpp.
Then look at file_preprocessed.txt.Code:C:\>cd "My Documents\programs\directory" C:\My Documents\programs\directory>g++ -E file.cpp > file_preprocessed.txt C:\My Documents\programs\directory>
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All this time for a ridiculous thread.
> Consider the xor swap instead then.
As Shakespeare would say, this is going from Bard to Verse.
http://c-faq.com/expr/xorswapexpr.html
If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
If at first you don't succeed, try writing your phone number on the exam paper.
Hey, I am just trying to understand the language and things you can do with it! Maybe I don't come up with the best questions, but can you please try to ignore the fact that they are ridiculous? I want to know the answer of the questions I ask, not that I shouldn't ask them, so please do not question my questionings.
Last edited by TriKri; 08-01-2006 at 02:09 PM.
That is an incorrectly written xor swap. The real one doesn't produce any faulty values.
Go on then, show us the "real one". Then explain how it's different.
Quzah.
Hope is the first step on the road to disappointment.
Don't be so cocky, it says "It attempts to modify the variable a twice between sequence points, so its behavior is undefined". The real one doesn't and hence the result isn't undefined.
Oh, so you're saying you can't write the "correct one", right? Yeah, I thought so. Shut the ........ up, get off the forum and stop wasting our time.
Quzah.
Hope is the first step on the road to disappointment.
You can leave if you want.
In other words, like I said, you can't write the "real one", because you're just making ........ up again. Have a nice ban.
Quzah.
Hope is the first step on the road to disappointment.
Obviously didn't read the rest of the c.l.c FAQ
If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
If at first you don't succeed, try writing your phone number on the exam paper.
