Avoid return statement in the middle - horror or not?

[Rob Grainger]

Personally, I have no real problem with returns in the middle of a function as long as there are no cleanup considerations, and as long as the procedure remains clear and readable. For cleanup issues, I believe C++ leads the way through RAII (Resource Acquisition Is Initialisation - RAII (Wikipedia), allowing code to be written in whichever manner makes it clearest to read - any resources are then guaranteed to be cleaned up on exit from the routine.

[supercat9]

The for-loop version is just plain nasty. It wastes a variable and a lot of code. Doing #define once while(0) and then

do {
some_code;
} once;

would avoid the wasted code. If one wanted to tag both ends of the loop to make clear what was going on, instead of just the tail, one could define some other word as a synonym for "do". Personally, though, I don't like using macros to alter the syntax of a language doing so will make practical something that would otherwise be impractical. To people familiar with do{}while(0); as a means of doing something once, that form will be as readable as anything else. For those unfamiliar with it, the macro would just add confusion. That it would be desirable for a language to include a feature to avoid silly always-true or always-false conditionals does not imply that it is desirable to kludge such features. BTW, if you really want your syntax, and if your code doesn't have to be thread-safe, you can limit the total number of extra variables program-wide to one:

#define once for(once_var=2;once_var>>=1; )

The global variable once_var will always be zero or one (doesn't matter which) except between the initial assignment and the initial test, so nested loops and recursion shouldn't pose problems. Still a horrible waste of code, but it should achieve the desired result.

[PIEBALDconsult]

supercat9 wrote:

The global variable once_var

Where do you declare it?

supercat9 wrote:

do{}while(0);

I've only seen that in the GCC documentation where it talks about "swallowing the semi-colon". I've certainly never seen it in production code, and I hope I never do. As others have also said, I don't use do/while, only while. And I don't write a loop that isn't a loop. Wait a minute... doesn't the 0 in while(0) have to exist somewhere as well?

[supercat9]

PIEBALDconsult wrote:

Where do you declare it?

I usually have a module with any global variables that are required by my macros. Not wonderful, but I don't know any better approach in C.

PIEBALDconsult wrote:

I've only seen that in the GCC documentation where it talks about "swallowing the semi-colon". I've certainly never seen it in production code, and I hope I never do.

When trying to write a macro that behaves like a void function but contains an 'if' statement, something like:

#define foo(x) do {if (x > 0) do_this();} while(0)

is clearer than:

#define foo(x) if (x > 0) do_this(); else

while nonetheless avoiding the difficulties associated with:

#define foo(x) {if (x > 0) do_this();}

or worse, the bug-prone

#define foo(x) if (x > 0) do_this()

which makes me cringe.

PIEBALDconsult wrote:

And I don't write a loop that isn't a loop.

What would be your preferred way of allowing a procedure to be done in multiple steps and abort at any step, while ensuring that any necessary cleanup would be completed? If you prefer a "goto" label to a do/while(0) structure with break statements, fine. That's actually my usual preference. Can you suggest anything better than the do/while(0) for people who dislike goto?

[PIEBALDconsult]

I don't mind it hidden in a macro; I expect to find odd things there, but I don't want to see it hung on the wall for all to see. Anyway, the original post's logic doesn't require anything like that.

[coolM]

In case of complex preconditions separate those to another function. This prevents structured-ifs and keeps the calling-function readable. If the conditions change (in thight iterative development this always happens), adaption gets easy.

bool ShouldDoSomething()
{
//no returns in middle of method, only on start
// or everywhere.. ;)
if(!flagA) return false;
if(!flagB) return false;
if(!flagC) return false;
if(!PromptUser() ) return false;
return true;
}

void callingFunction()
{
if( ShouldDoSomething() )
{
DoSomething();
}
else
{
DoOtherThing();
}
}

[PIEBALDconsult]

Then why not:

bool ShouldDoSomething()
{
return ( flagA && flagB && flagC && PromptUser() ) ;
}

which is much easier to read? :-D

[coolM]

you're right... got a bit infected by the horror around.

[notmasteryet]

Be aware of Junioria Developerus animal. Those species may decide that PromptUser() && flagA && flagB && flagC looks prettier. :) Cyclomatic complexity for && and if is the same. Some people believe that cyclomatic complexity number is directly related to code maintenance. And in this thread we did not really lower the number. Is the original code fine as is?

[PIEBALDconsult]

notmasteryet wrote:

Junioria Developerus

I suppose that would be a reason not to distance the tests from the code that uses it. And not to use a lot of negation.

[johannesnestler]

You are depending on the order of evaluation of your if-statement for your logic to work. Will the PromptUser() operand be evaluated before the entire set of && operations are performed? I think C++ has an "undefined order of evaluation". Who knows. It should be irrelevant. Writing code that depends on order of evaluation is bad programming practice, regardless of language. Sorry, but not knowing how your programming language works is bad practice (operator priority is very important in every language!). And depending on the order of your evaluations is the usual case in real world programming-logic. (I think you are mixing up here with the | and & operators and something a teacher told you once...). I think C++ has an "undefined order of evaluation". Who knows No - and I!!! ;P

[Megidolaon]

Ever thought about using &&?