Avoid return statement in the middle - horror or not?

[PIEBALDconsult]

From the ANSI C99 spec I have: " 6.5.13-4 Unlike the bitwise & operator, the && operator guarantees left-to-right evaluation; there is a sequence point after the evaluation of the first operand. If the first operand compares equal to 0, the second operand is not evaluated. " Even Ritchie's C manual from 1974 says it's left-to-right. (It appears that B does not have these operators.) In the K&R book, they're talking about a[i]=i++, not the && operator, plus that's a very old book. You may certainly go right ahead and write code any way you like... I do.

[PIEBALDconsult]

Having one return statement is still a worthwhile goal. You just have to look at it both ways and decide which is "better" in each individual case. I don't recall encountering any situations that required multiple return statements.

[Michael Dunn]

You can't make a rule like that because there is no one correct rule that works for every single function you're going to write in your life. Well, you can make the rule, but doing so will be counter-productive. Why create a state machine with local variables in a function (and don't forget to test every possible state!), just to avoid using a perfectly valid language feature?

--Mike-- Visual C++ MVP :cool: LINKS~! CP SearchBar v3.0 | C++ Forum FAQ I work for Keyser Söze

[Andrew Torrance]

Single exit , single entry . Its a mantra that leads to clarity how about if( !FlagA || !FlagB || !FlagC) // Select Variant on !Flagx or Flagx == false depending on language DoOtherThing(); else { if(PromptUser()) DoSomething(); } Not a horror though. My use of single entry and exit points in functions leads to more debates than anything. (My how the winter nights fly by)

[Robert C Cartaino]

Andrew Torrance wrote:

if( !FlagA || !FlagB || !FlagC) // Select Variant on !Flagx or Flagx == false depending on language DoOtherThing(); else { if(PromptUser()) DoSomething(); }

...except if PromptUser() fails, you also have to execute DoOtherThing(). So you need to add to your code:

if( !FlagA || !FlagB || !FlagC) // Select Variant on !Flagx or Flagx == false depending on language
DoOtherThing();
else
{
if(PromptUser())
DoSomething();
else DoOtherThing();
}

[PIEBALDconsult]

How is that better than what I posted?

[Mladen Jankovic]

Robert.C.Cartaino wrote:

Writing code that depends on order of evaluation is bad programming practice

If order of evaluation is not defined by the specification of the language, which is not true for logical operators in C/C++. According to your statement one should not write something like this:

if( node && node->value )
node->value->Do();

Instead you need to have another if for this simple operation even if the previous example is perfectly legal and clean and the desired behavior is guaranteed by the language specification. Well I guess that the only bad programming practice here is that someone introduces unneeded code because he doesn't trust/know language.

[Genetic Algorithm Library]

[PIEBALDconsult]

Indeed. And should we question the order/precedence of the other operators as well? Can we trust 3 + 4 * 5 to return 23? or might it return 35 once in a while? I'm all for adding parentheses for clarity, but I don't get that confused with necessity.

[Ben Fair]

Yes, he just inverted the boolean logic and made it worse in my opinion. if(!FlagA || !FlagB) is essentially the same as if(FlagA && FlagB) but I'd rather see the latter and that's how I'd do it in my code.

Keep It Simple Stupid! (KISS)

[geoffs]

It's not. Your code was how I would have done it...

[User 167261]

it all depends on how much coffe i've had for the day...

do or do not, there is no try

[PIEBALDconsult]

Drinking coffee leads to good code. Drinking "energy drinks" leads to poor code.

[FatBuddha]

Assuming that there is more processing going on than this example indicates, I would use a do-while-false loop:

do{
if(!flagA)break;
if(!flagB)break;
if(!flagC)break;
if(!PromptUser())break;
}while(0);

DoOtherThing();

This is the sort of thing that I routinely do with COM programming where I need to check the success of pretty much every single method call. It means that I don't have a crazy amount of indenting, and it's much cleaner for me or somebody else to understand and modify later. I can highly recommend it.

None

[rfidel]

Not sure if this made one of the previous replies, but what I found works best, and is easy to follow, is to iteratively step thru what I do not want, making use "else if" statements. After weeding thru all the crap, then what I am left with, is (usually) what I want. if(!flagA) { DoOtherThing(); } else if(!flagB) { DoOtherThing(); } else if(!flagC) { DoOtherThing(); } else if(!PromtUser()) { DoOtherThing(); } else { DoSomething(); }

[PIEBALDconsult]

That's simply the first snippet inverted and made even uglier. It's still a maintenance nightmare.

[PIEBALDconsult]

Where's the call to DoSomething? I'm pretty sure that's not applicable to the original post.

[FatBuddha]

Doh - I was looking at the second code listing. Assuming that there is lots of other stuff going on between the flag tests, and there is a need for clean-up code (thus don't want to use return), I'd use the same system with a flag:

//Figure out what to do...
bool doSomething = false;
do{
if(!flagA)break;
if(!flagB)break;
if(!flagC)break;
if(!PromptUser())break;
doSomething = true;
}while(0);

//...then do it
if(doSomething)
DoSomething();
else
DoOtherThing();

None

[PIEBALDconsult]

Still looks like a potentially infinite loop.

[Manish K Agarwal]

I usualy perfer "goto cleanup" statement (where cleanup is lable inside the function) instead of making code hard to read.

Manish Agarwal manish.k.agarwal @ gmail DOT com

[Marcello Faga]

Georgi, I agree with you. "Return in the middle" is an horror! X|

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