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| Will this code work? |
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type568
Member #8,381
March 2007
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#include <stdio.h> #define FATAL_ERROR {int* a=NULL; *a=1;} int main(int argc, char** argv){ if(1==0) FATAL_ERROR return 0; }
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Thomas Fjellstrom
Member #476
June 2000
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That specific code might work. You really don't want to try and access invalid pointers like that. just use abort() or even exit() instead. Also, theres an issue with the {}s. If you try and put it in certain places, you'll start to get confused. -- |
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StevenVI
Member #562
July 2000
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It was easier to open up the Allegro.cc forums to ask this rather than putting it into a compiler? Define "work". __________________________________________________ |
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type568
Member #8,381
March 2007
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Thomas Fjellstrom said: Also, theres an issue with the {}s. If you try and put it in certain places, you'll start to get confused. I edited the first post before your reply. Is it ok now? StevenVI said: It was easier to open up the Allegro.cc forums to ask this rather than putting it into a compiler? It compiles. Quote: Define "work". No. Append: That's not coz I don't want to.
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Jeff Bernard
Member #6,698
December 2005
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My initial thought was no... {"name":"599918","src":"\/\/djungxnpq2nug.cloudfront.net\/image\/cache\/8\/7\/87aa5d17258a1186c51946c1ded42232.jpg","w":1024,"h":768,"tn":"\/\/djungxnpq2nug.cloudfront.net\/image\/cache\/8\/7\/87aa5d17258a1186c51946c1ded42232"} EDIT-- ah, but now now I see this has to do with Matthew... -- |
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Thomas Fjellstrom
Member #476
June 2000
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type568 said: I edited the first post before your reply. Is it ok now? It looks the same to me You generally don't want to put bare {}s in a define. do something like: #define BLAH do{ codehere }while(0) instead. Then you can use it like so: if(foo) BLAH; -- |
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Billybob
Member #3,136
January 2003
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Yes. And no, you don't want to do it.
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Vanneto
Member #8,643
May 2007
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Hmmm, made me think, what if: if (1 == 0) { } Actually returned true? What would that mean? In capitalist America bank robs you. |
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GullRaDriel
Member #3,861
September 2003
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It will never return true because it's the same if "a=1;b=0; if(a==b)" would have returned true: nothing would have worked as expected. "Code is like shit - it only smells if it is not yours" |
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BAF
Member #2,981
December 2002
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What if I were a millionaire? What would that mean? |
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GullRaDriel
Member #3,861
September 2003
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That you are still asleep and dreaming, BAF ;-) "Code is like shit - it only smells if it is not yours" |
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BAF
Member #2,981
December 2002
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type568
Member #8,381
March 2007
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Vanneto said: Actually returned true? What would that mean? That would mean a FATAL ERROR I suppose..
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anonymous
Member #8025
November 2006
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Vanneto said: Hmmm, made me think, what if: if (1 == 0) { } Actually returned true? What would that mean? That would basically mean the compiler malfunctioned, and given such a compiler, god knows what FATAL_ERROR would do. |
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type568
Member #8,381
March 2007
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Thomas Fjellstrom said: You generally don't want to put bare {}s in a define. I guess last question in this thread.. Thomas, is there a real reason not to put a {} in a define?
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GullRaDriel
Member #3,861
September 2003
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No real one except it's unneeded. They're needed in case of a if/do/while/for statement inside the #define, but you gain nothing adding {} in some simple statements as int *it; it=NULL, except huge problem spotting out the bug if you forgot to close/open a {} "Code is like shit - it only smells if it is not yours" |
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Audric
Member #907
January 2001
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I've used similar code (writing at NULL) to test my signal handler. |
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GullRaDriel
Member #3,861
September 2003
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Audric: I use kill -signal for that kind of things. "Code is like shit - it only smells if it is not yours" |
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type568
Member #8,381
March 2007
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Actually, I DO need the {} in the define, as otherwise the above code won't even compile. As the macro is just replaced with it, and only one line is scoped in to an if statement(and the a won't be declared identifier).
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GullRaDriel
Member #3,861
September 2003
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You DO need it because of your implementation. Keep in mind that #define are just preprocessing substitution. Doing so would also work: #include <stdio.h> #define FATAL_ERROR int* a=NULL; *a=1 int main(int argc, char** argv){ if(1==0) { FATAL_ERROR; } return 0; }
Plus your macro is evil. "Code is like shit - it only smells if it is not yours" |
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type568
Member #8,381
March 2007
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That's what I meant.. But I wanna be referring to a single line MACRO as to a single line.. I still wonder what did Thomas mean though. Append: GullRaDriel said: Plus your macro is evil.
Is my if statement less evil?
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Thomas Fjellstrom
Member #476
June 2000
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type568 said: I still wonder what did Thomas mean though. Well for one, when you look at a bare macro do you always remember it has {}s surrounding it? What if you put it some place that causes a compiler error? Will you remember then that it is a block? I already gave the proper alternative. a do{CODE HERE}while(0) construct. That way its a statement, and not a block. And can be used in any place a regular statement can be, without any problems. -- |
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Billybob
Member #3,136
January 2003
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Thomas Fjellstrom said: That way its a statement, and not a block. I have a feeling you are correct, but I am curious for an example as well. An example of where his implementation would cause an error, and yours would not.
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Audric
Member #907
January 2001
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Example (google on "define while 0"): |
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type568
Member #8,381
March 2007
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Thomas Fjellstrom said: Well for one, when you look at a bare macro do you always remember it has {}s surrounding it? What if you put it some place that causes a compiler error? Will you remember then that it is a block? That's it.. I can't imagine such a case. Unless I decided to do some assignment works out of scope of a function.. However, is not this: #define FATAL_ERROR {int* a=NULL; *a=1;};
Easier? I didn't check this one, but I'm quite sure that MSVC(latest one) at least won't give errors to that.. Furthermore, I encountered a ;; in my code, without any warnings, and of course without side effects as well. a ; is a ;, it doesn't harm if doubled, unless really misplaced.
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