On Thu, Mar 12, 2009 at 11:29 PM, Dave Korn <dave.korn.cyg...@googlemail.com> wrote: > James Dennett wrote: >> On Thu, Mar 12, 2009 at 4:56 PM, Robert Dewar <de...@adacore.com> wrote: >>> Nathan Ridge wrote: >>> >>>> Why does gcc not give an error about this? >>>> If I compile with "-Wall", it will give a WARNING saying >>>> "control reaches end of non-void function". >>>> However, shouldn't it be an ERROR to return nothing >>>> from a function that's supposed to return something? >>>> Does this not result in undefined behaviour? Why goes gcc allow it? >>> Because the standard does not make this an error, you can't tell >>> if anyone needs a result, perhaps function is always called in >>> a void environment. >>> >>> A warning is all you can get, always pay attention to warnings! >> >> The standard does make it an error, in that if such a function >> (meaning a function that unconditionally falls off the end, when >> declared to return a value) is called _at all_ then undefined behavior >> results. > > No, unless I have missed something.. Not if it is merely called: only if > the return value is *used* (n1256 #6.9.1.12).
This appears to be a difference between C and C++. Unfortunate. 6.6.3 [stmt.return]/2 of N2800 says "Flowing off the end of a function is equivalent to a return with no value; this results in undefined behavior in a value-returning function." > Freestanding implementations > may use this to effectively allow a void main(). There's no need for such trickery; main is special, and has an implicit "return 0;" (for both C and C++, I believe, since 1999). IIRC, C allows freestanding implementations to allow "void main" as an extension (and C++ does not). -- James
