Older blog entries for redi (starting at number 16)

20 Sep 2002 (updated 22 Sep 2002 at 01:22 UTC) »

fxn: re username filters in MyAdvogato, I'm not actually desperate for username filters, all I need to do is resist the temptation to read the latest stupid troll by you-know-who, it's sort of a sick compulsion to see what crap he'll spew next, and just skipping those entries is much easier and saves the trouble of maintaining an ignorelist external to my head. As I understand it your diary ratings report shows other users' ratings as seen by you. If you've rated someone directly the rating will appear with a confidence of 1, otherwise the confidence is a function of the distance (and certs?) between your user and the rated user. Update: It seems that if you've cert'd user A, and A has rated B's diary, then the rating you see for B is strongly affected by A's rating (in other words by cert'ing someone you've implied you trust their ratings more significantly than some random user. Presumably this trust of ratings propogates outwards with the web of cert's.

How I Learned to Stop Reinventing the Wheel and Love UNIX

This is going to read like a sales-pitch written by a marketing dept. but I'm just trying to get some ideas to coalesce. It's been at the back of my mind for a while, but I've only recently realised just how easily PStreams lets you tie together UNIX utilities in the same way as pipes do on the command line or in a shell script, letting you use existing tools directly inside your C++ program. Noone writing a scripting language would write their own text manipulating functions, they'd use an existing tool such as sed, but C++ programmers all-too-often reinvent the wheel, because to call external programs you have to set up the necesary pipes, call fork(), exec(), wait4() etc. With PStreams all you do is instantiate a single object, which takes care of calling and error-checking all those functions, and then you write to and read from the process as with any IOStream object. To be honest I'm rather surprised this hasn't been done a thousand times already. While I was writing it I read an article in CUJ Binary Code Reuse in a Linux Environment where "Traditional UNIX-like filters meet C++" which is pretty similar, but the interface is IMHO far less natural than with PStreams, and it doesn't map as well to the familiar syntax of pipes on the command line. Somehow I seem to have almost accidentally created a useful and powerful way to write C++ programs as you'd write shell scripts, and AFAIK there's no existing Open Source equivalent. Blimey, can that be right? Surely not. All I was doing was scratching an itch.

My plans for the library are to abstract the creation and control of the new process from the I/O facilities of the existing classes, which would provide a general-purpose process management class for C++, that could be used to implement the PStreams classes. Someone please stop me now if this has been done (well) already.

It's a good thing this is only a tiny project (in terms of lines of code) as I'd never finish it otherwise. It'd be done in a week if I stopped getting wasted every night and finished adding buffering to the stream classes. Not tonight though, it's friday, so I'm going for a pint.

18 Sep 2002 (updated 18 Sep 2002 at 17:53 UTC) »
joy: FreeBSD 4.6 uses its own release of GCC (2.95.4 20020320 [FreeBSD]), which includes <sstream> and has a standard-comforming std::string. Hoorah! Since our development where I work is done on FreeBSD and we can't just switch to GCC 3 (adding std:: quals alone would take weeks!) this is great news as far as I'm concerned. I can track down and remove all my comments along the lines of "have to do it this way because of GCC 2.95". This has also reminded me to check if GCC 3 supports covariant return types on virtual functions yet...

bugs: Found (and reported, of course) another possible bug in MySQL. I still need to find time to prepare a test case for an issue that was crashing our web sites, where DELETE FROM tbl_name WHERE column IN (...) doesn't complete. Also found what I think is a security hole in FreeBSD, but I need to do a bit of testing and check if it's still there in 4.6 to be sure. (Updated: I should point out the most likely explanation is I'm completely wrong, so don't panic :)

fxn: re filters in MyAdvogato, I think name-based filters are my most wanted feature. 'nuff said.

Going home in a minute to watch some footy and maybe hack some PStreams.

I'm adding buffering to the PStreams stream buffer class (it's currently unbuffered, which isn't an oxymoron, honest) and have found some errors in Langer & Kreft's IOStream book so I went to find the errata, and found that my first printing has quite a few errors. This isn't the first time I've wished I could exchange a 1st printing for a discount on a corrected one, as these things ain't cheap. I'll have to be more patient and wait for a reprint of the next new book I want to buy. Unless I find way to patch hardcopy I'll have to take sharp pencil to the book tomorrow.

I've also started abstracting the creation and control of the child process to a separate class to separate the responsibilities of the streambuf. I keep being pleased with the results of applying received programming wisdom even on such a small set of classes as I'm writing. The code is so much simpler when the design is right.

14 Sep 2002 (updated 11 Oct 2002 at 14:33 UTC) »

Finally got djbdns running at home. For some reason it took me ages as I kept putting the wrong addresses in resolv.conf, or the dnscache environment, or something else over and over again. I think setting bind up would have taken me longer, and I wouldn't have been confident I'd done it securely. Learning a bit about DNS doesn't really make up for being ill and missing a band on a friday night, but my computer's a bit better now. bah. I think I quite like DJ Bernstein's svscan alternative to init.d for starting and stopping services.

bgeiger: to get Mozilla to do a tooltip style popup use the title attribute. The standard specifically says it can be rendered as a tooltip in visual browsers, it says no such thing for alt. title can also be applied to any element, not just <img>, try it with <span> around some text (in a good browser anyway). If you must use tooltips you can put the same text for alt and title to do a tooltip that works in Netscape4, Mozilla, Konqueror, Opera and IE. And that's why Mozilla won't change. A more accessible reference here
Update: oops, that "more accessible reference" was a local file on my hard drive! Fixed to point to the online version

11 Sep 2002 (updated 14 Sep 2002 at 15:22 UTC) »

A fair bit of work on PStreams over the weekend, not much sleep, but lots of big ideas for where to take it once the current work is done and it's feature complete. More on this soon, once I've thunked a bit more and need to make some notes for myself. I had to get out of bed the other night to scribble some ideas down that had come to me as I was drifting of to sleep. I would have been able to remember them fine in the morning, but they were burning a whole in my head and I had to write them down to so I could go to sleep. I've learnt a lot from doing this project (what's used in the code is only a fraction of it) and it's interesting to look at the progression of my ideas and how they and the classes coalesced into the current design. Interesting for me anyway. I don't expect anyone else is even reading this. Go read a good book instead if you are, you'll get a lot more out of it.

Reminder: track down SIGPIPEs on Solaris and see why they're raised there and not on other platforms. Hmm.

Reminder: check the latest code into CVS. It's functionally better than the previous version, has more features, and I'll not be able to implement my big ideas for the future until it's in. done

Some responses...
goingware: Happy birthday to your mother and aunt. I'm about to go see a friend who's birthday it is today as well. I don't think he's been looking forward to it much, with the other significance this date has now. He owns a pub though, so I imagine we'll all get into birthday mood eventually. You can't let every birthday be ruined because something tragic happened on that date. There's no logical reason why today should be any more upsetting than the 100 day anniversary, or 1000 days. But that's logic for you.
fxn: Glad to hear there'll be a filter on recentlog. I'm not sure I'd use it often (some unrated people have interesting things to say) but it could be useful sometimes. Will it only work on diary ratings? Or on cert level and/or username as well? The diary ratings include other people's ratings, which might someone who's scribblings you enjoy reading are filtered out because everyone else has rated them down. Ignore me for now, I'll have a look when you release it.
mtearle: I got someone to download OpenOffice to install at their workplace today. I'd mentioned it before, and he phoned me up to ask about it, as he didn't want the hassle of finding out whether they were licensed to install another copy of Office, and the hassle of using Office! I hope he's happy with it.

4 Sep 2002 (updated 4 Sep 2002 at 18:16 UTC) »
mathieu: I was only half paying attention. Yes, line 3 might not behave as expected. You probably know this already, but I'm explaining for my own benefit as much as anything! The array initialisation in line 2 creates an array on the stack, of size strlen("this is a string you can modify")+1, and copies the characters in the string literal into the array. Line 1 assigns the address of the string literal to p. a is therefore an array of non-const chars that can be modified and line 3 is fine. p points to the actual string literal, which is an array of non-modifiable chars and so line 4 invokes undefined behaviour (on my OS the literal is in the text section of the executable, which can't be modified, but that's an implementation detail).

I agree that the code shouldn't be valid; if string literals in C had type const char [] instead of being "non-modifiable char" [] the problem wouldn't exist. Bjarne Stroustrup's doing an interesting series of articles in the C/C++ Users Journal at the moment about C/C++ compatibility and why C++ retains this sort of gotcha from C, rather than fixing the mistake and abandoning compatibility.

bjf: Have you looked at WML?
3 Sep 2002 (updated 3 Sep 2002 at 10:35 UTC) »

Passed the technical test thing I took last week for a job, so I'm in for an interview. I'm quite surprised, as although the test was very easy, I spent too long on the C++ section crafting the perfect answers and stupidly ran out of time and didn't write anything for some other chunks of it (and wrote complete rubbish for the database bit as I rushed to scribble something down.) Nevermind, I'm the only person to get through to the interview. Which is nice.


You're modifying a string literal. String literals in C have type (non-const) char*, but are non-modifiable, doing so invokes the dreaded undefined behaviour, so a coredump isn't too bad, you should think yourself lucky you didn't rupture a hole in the fabric of the universe. In C++ string literals are const, but as Stroustrup The Wise explains:

The type of a string literal is "array of the appropriate number of const characters," so "Bohr" is of type const char[5].
A string literal can be assigned to a char*. This is allowed because in previous definitions of C and C++, the type of a string literal was char*. Allowing this assignment of a string literal to a char* ensures that millions of lines of C and C++ remain valid. It is, however, an error to try to modify a string literal through such a pointer:
void f()
    char* p = "Plato";
    p[4] = 'e';  // error: assigment to const; result is undefined
This kind of error cannot in general be caught until run-time, and implementations differ in their enforcement of this rule.
Stroustrup, C++PL3E, ยง5.2.2


"Programming is one of the most difficult branches of applied mathematics; the poorer mathematicians had better remain pure mathematicians."
Edsger Dijkstra
I'm not sure I agree, but who am I to argue with Dijkstra?
28 Aug 2002 (updated 12 Sep 2003 at 08:42 UTC) »
xach's Nigeria 419 Scam beats the hell out of the original. Cheers for a giggle, xach!
I guess it's the online equivalent of inviting Jehova's Witnesses in and preaching to them rather than the other way round, just to see if you can twist their melons. My brother and I tried this with a couple of Mormons who stopped us in the street on friday night (or all times!)
Them: "Have you heard of the Church of Jesus Christ and the Latter Day Saints?"
Me: "Yes, I have actually, but it's not my bag. Want a toke on this? No, I thought not."
Bro: "Are you familiar with Sufism? Read any Idris Shah? Oooh, let me enlighten you..."
I have nothing against people who've "Got Faith", but I resent their assumption that everyone else is spiritually ignorant and is just waiting to be shown the light.
Oops, back to software...

Found an ICE in mainline GCC, but probably didn't need to include preprocessed unistd.h file in the report since test case doesn't use anything from it (it used to, but I reduced it). Or maybe it doesn't ICE without unistd.h? Should have been paying more attention when I reported it - this diary entry is to remind me to check tonight!

Another reminder: fix JavaScript on my sidebars page: left "//" out of baseurl variable. Doh! Still works though. Mozilla won't let you add sidebars from local URLs, neither file://fnordikus nor http://localhost/ting is allowed to be used as a sidebar. I wonder why not. When I'm at home I want to have my sidebars loaded from the localhost, not across my dialup connection. Workaround: use external hostname instead of localhost.

(That's enough rambling nonsense - Ed.)

Update: The 3rd Annual Nigerian EMail Conference

What have I been up to recently...

Fixed some dumbass copy'n'paste errors in PStreams - I should make time to work on it, rather than trying to do it in 5 mins late at night

Started converting the libstdc++ web pages to XHTML. It's a fairly simple process using sed, sh, vim and some scissors and glue.

Got annoyed at the MySQL people, but resisted the urge to fire off an angry email. In version 3.23.48 (I think) they made the mysqldump utility generate output that causes an error when you try to import the dump into any earlier version. Not the sort of change I expect from a minor minor revision, especially as it wasn't mentioned in the ChangeLog. The change was in the meaning of the --opt option, which from 3.23.48 onwards has the additional meaning of "make the output incompatible with all previous versions". Nice. No need to document that, no no no. You'd spoil the fun of letting people find that out for themselves. The option's supposed to have some use for the development version, 4.0, but for the stable 3.23 series it's ignored, or for older versions it means "cause an error".

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