Hello Ian, On Mon, 26 Oct 2015 10:07:24 +0000, Ian Campbell <ijc+ub...@hellion.org.uk> wrote: > On Sun, 2015-10-25 at 22:16 +0100, Albert ARIBAUD wrote: > > Hello Ian, > > > > On Sun, 25 Oct 2015 19:22:00 +0000, Ian Campbell > > <ijc+ub...@hellion.org.uk> wrote: > > > On Sun, 2015-10-25 at 14:22 +0100, Albert ARIBAUD wrote: > > > > On Sun, 25 Oct 2015 12:40:45 +0000, Ian Campbell > > > > > Doesn't the bool return type already cause that to happen? > > (from the > > > > > PoV of the caller at least) > > > > > > > > When all is said and done, a C bool is a C int, > > > > > > Not if it is a _Bool (via stdbool.h or some other way). > > > > > > A _Bool is always either 0 or 1, and scalar value which is > > converted to > > > a _Bool is converted to either 0 or 1. > > > > > > > So no, types, bool or otherwise, do not cause any implicit '!!' > > to > > > > happen. > > > > > > I believe this is not correct when _Bool is used. > > > > > > In u-boot a bool is indeed a _Bool (or at least I don't see any > > other > > > typedef's and I can see various includes on stdbool.h, I therefore > > > didn't feel the need to check how bool is arrived at in this > > particular > > > file). > > > > What you write is possibly correct for C++, but certainly not for C, > > for which booleans are integers, with no compiler-enforced constraint > > on their value domains. > > I know next to nothing about C++ so I am certainly not confusing things > with that. > > The _Bool type in C99 is an integer which may take on exactly the > values 0 or 1. Since the code which started this subthread was using > "bool" from <stdbool.h> it is _Bool which is being discussed here. > > The actual standard costs money (and is therefore unlinkable) but > http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1256.pdf is a late > draft and I believe this aspect is unchanged. Section 6.3.1.2 is one > relevant part explaining that a _Bool must always be either 0 or 1: > > When any scalar value is converted to _Bool, the result is 0 if the > value compares equal to 0; otherwise, the result is 1. > > Many of the other clauses dealing with Integers (e.g. 6.3.1.3.1) have > had "other than _Bool" or some similar wording added to them since > _Bool does indeed behave a little differently. > > So I'm afraid I disagree with your statement, at least for C >= C99 (I > can't recall if _Bool was in C89, but I think the answer is no).
I stand corrected: I've just checked it, and the conversion does indeed happen on return -- at least gcc 5.2.1 -- even when, like in U-Boot build files, c99 standard compliance is not specified. If older GCCs (up to a point: how old a gcc are we wanting to support?) also work this way too, the '!!' is indeed unneeded. > Ian. Amicalement, -- Albert. _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de http://lists.denx.de/mailman/listinfo/u-boot
