On Wed, Jan 1, 2020 at 10:57 AM ToddAndMargo via perl6-users <perl6-users@perl.org> wrote: > > On 2020-01-01 01:58, JJ Merelo wrote: > > > > El mar., 31 dic. 2019 a las 21:56, ToddAndMargo via perl6-users > (<perl6-users@perl.org>) escribió: >> >> On 2019-12-31 09:17, JJ Merelo wrote: >> > Hi, >> > >> > El mar., 31 dic. 2019 a las 5:54, Todd Chester via perl6-users >> > (<perl6-users@perl.org <mailto:perl6-users@perl.org>>) escribió: >> > >> > Hi All, >> > >> > >> > https://docs.raku.org/language/nativecall.html#Passing_and_returning_values >> > >> > Did anyone else discover the mistake, hopefully not the hard way like I >> > did. Anyone get weird gibberish printed out like I did? >> > >> > my$string="FOO"; >> > # The lifetime of this variable must be equal to the required >> > lifetime of >> > # the data passed to the C function. >> > my$array=CArray[uint8].new($string.encode.list);v >> > >> > The mistake is that "C" strings are terminated by a chr(0) -- in >> > "C" terms chr(0) is called a nul or 0x00. >> > >> > If you don't terminate your C string, the reading functions keep >> > careening >> > until it finds a chr(0). You have to tack a chr(0) onto the end. >> > >> > my$array=CArray[uint8].new($string.encode.list); >> > $array [$array.elems] = 0; >> > >> > $array should be 70 79 70 0 not 70 79 79 >> > You can test this with `say "$array"` (include the quotes). >> > >> > Maybe JJ will pick up on this and get it fixed. >> > >> > >> > >> > I don't always read this list, but I do read issues. If you put it >> > there, it will be definitely get addressed when possible. >> > >> > -- >> > JJ >> >> >> Hi JJ, >> >> I have a rule about not posting to that list, so maybe > > > I could answer that with I will not address issues that are not raised in the > GitHub repo (which is not a list, BTW), but anyway, here you go. The thing > is, first, that the example has little to do with the structure of the string > itself; it focuses on the fact that the string has to be encoded. But anyway, > let's check if that is true, with this little example: > > ------ >8 ---------- const-char.c ---------------------- > #include <stdio.h> > > void set_foo ( const char *foo) { > printf("%s", foo); > } > ----------------- 8< -------------------------------------- > > And this Raku script that uses it > > -------------------------- >8 --------------- null-terminated-or-not.p6 > -------------- > use NativeCall; > > my $string = "FOO"; > my $array = CArray[uint8].new($string.encode.list); > sub set_foo(CArray[uint8]) is native('const-char') { * } > set_foo( $array ); > ----------------- 8< -------------------------------------- > > This works without a glitch, printing FOO to the terminal. As a matter of > fact, $array.elems returns 3, so its "encode" is not actually adding any > null-termination at the end. I'm no expert in C myself, and have not been for > at least 25 years. But I know stackoverflow, which says > (https://stackoverflow.com/a/1253336/891440) > > Why do C strings work this way? It's because the PDP-7 microprocessor, on > which UNIX and the C programming language were invented, had an ASCIZ string > type. ASCIZ meant "ASCII with a Z (zero) at the end." > > Is this the only way to store strings? No, in fact, it's one of the worst > ways to store strings. For non-trivial programs, APIs, operating systems, > class libraries, you should avoid ASCIZ strings like the plague. > > > Plagues are bad. Let's avoid them for the upcoming year. Other than that, > happy new year to every one. > > -- > JJ > > > Hi JJ, > > Wow, you spent a lot of time on that. Thank you! > > You are of course correct. > > The example works and that is the end of it. So no > mistake to be addressed. > > You are a teacher. Would you have wrote that example > with out addressing the nature of a "C" string and why > it requires a nul at the end? > > You are a teacher. Would you have given an example that > only worked in the example? > > You are a teacher. What would you have made the > purpose of that document? To teach how to use the > module? Or so just put down things with no practical > application? "It is intuitively obvious and left up to > the student to figure out on his own?" > > This is what happens in reality when you do not add the > nul to the end of a "C" string. C just keep careening > until it finds a nul. Here you go: > > > > > So you are 100% correct in your assertions. And why > this error will not be corrected. And a good example > of why I don't post there anymore. > > -T
Hi Todd, Isn't the point of the NativeCall interface to call native C code? By changing that requirement, won't it be harder for "native C" programmers to contribute to the Raku/Perl6 ecosystem? That being said, maybe an experienced C programmer might consider contributing a "NativeCall Linter" module to the Raku/Perl6 ecosystem. Best Regards, Bill. P.S. Following on Richard's remarks, maybe you can place the actual code for your modules into one or more Github repositories? And you/we can use the mailing list for extensive discussion (beyond what people might ordinarily consider "Github issues")?
