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User profile for user: Tron55555
Tron55555 Author
User level: Level 2
181 points

break statement does not work outside of switch or loop?

I was just messing around in Xcode and I discovered that, when I tried to use the break statement to exit a block of code, I got an error ("break statement not within loop or switch"). I thought the break statement was supposed to be able to be used to exit any block of code at any time, so I opened my Mac OS X Programming book by Wrox (a bit outdated, uses older version of Xcode/Interface Builder, but applicable enough), and the book confirmed that I should be able to use the break statement within any block of code, not just switch/case construction and loops. I assume something has changed in the newer version of Xcode since this book has been published, but I'm curious, so can anyone explain this to me? Thanks!

MacBook, Mac OS X (10.5.7)

Posted on Aug 31, 2009 2:14 AM

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User profile for user: etresoft
etresoft
User level: Level 9
53,420 points

Posted on Aug 31, 2009 9:56 AM

It sounds like the book is wrong. 'break' will only get you out of the innermost loop or switch. You can use 'return' to exit out of a function at any time.
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User profile for user: Tron55555
Tron55555 Author
User level: Level 2
181 points

Sep 1, 2009 1:44 AM in response to Tron55555

Yeah, that seems to be the case, and that's the only way I've ever used "break," but I did think it could be used to exit any block of code, especially having read it in the book I have. The book is Mac OS X Programming by Wrox, and on page 175 in the "The C Language" chapter, it says:


"break" is not only useful for "switch" and "while" statements; it can actually be used anytime you want to escape a block of code enclosed in braces. Execution is immediately transferred to the closing brace, and continues from there."

Anyways, I guess it is possible that in some older standard of C the "break" statement was allowed in these cases, since I can't imagine the book being out and out wrong, but you're right, it certainly seems to be -- interesting...
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User profile for user: xsmasher
xsmasher
User level: Level 1
105 points

Sep 1, 2009 8:37 AM in response to Tron55555

Sounds like your book is mistaken - I checked the K&R C book, and section 9.6 (Jump Statements) says "A break statement may appear only in an iteration statement or a switch statement, and terminates execution of the smallest enclosing such statement".

And it makes sense too - you can "escape" from a method with "return" , and you can skip code in other situations with an if/else. I don't know what a "break" outside a case would be expected to do.
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User profile for user: etresoft
etresoft
User level: Level 9
53,420 points

Sep 1, 2009 9:51 AM in response to Tron55555

'break' is really only a restricted form of 'goto' anyway. Ideally, you want a single point of exit from any block of code. You should really only use 'break' in a switch statement because that is the only way to make it work. In any other context, there are better ways to accomplish the same thing. The same applies to 'continue'.
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User profile for user: Tron55555
Tron55555 Author
User level: Level 2
181 points

Sep 4, 2009 11:24 PM in response to Tron55555

Thanks for the replies, guys. I've been hearing so many people make reference to K&R in the threads I've started here that I figured I'd buy a copy. Anyways, it gets here today, so I figure I'll be able to save some time and effort and refer to it myself for some of these questions I have. Thanks again for your posts.
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break statement does not work outside of switch or loop?

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