Bit of a techie one this, but how C++ handles its run time type casting is clever and useful but can be less than intuitive. This trap, I have fallen into more than once, is an obscure one you may like to ponder and save away for when it bites you. I certainly fixed the problem quicker the second time I encountered it!

class Dad {
virtual void method() { print(”In class dad”);}
virtual void otherMethod() { print(”Do something”);}
}

class Son::Dad { // class inheriting from dad
virtual void method() { print(”In class son”);} // this method is over ridden
}

main(){
class Son son;
class Dad *ptr;

ptr = &son;
ptr->method(); // even though type is Dad, this will print “In class son” because the late binding knows it’s really a “son”
ptr->otherMethod(); // this will print “Do something” because the late binding knows it’s really a “son” but son doesn’t have an otherMethod of its own
}

That’s the kind of things we programmers do a lot - not because we like print out the class names but because the classes we use are more useful - say class Employee and classes Engineer and Salesman that both inherit the basic methods (holiday(), pay() etc.) but do different things for other methods (work(), think() etc.).

Everything is nice until you need to change the code (that could be the definition of my job really!)

You need to add a value to “method” so you change the code to:

class Dad {
virtual void method(int N) { print(”In class dad with value %d”, N);} // add parameter
virtual void otherMethod() { print(”Do something”);}
}

// Son stays the same

main(){
class Son son;
class Dad *ptr;

ptr = &son;
ptr->method(99); // this now prints “In class dad with value 99″ because Son doesn’t have a method called method that takes a parameter so I must want the one in Dad.
}

That should be obvious(!), what has bitten me is when I’ve changed the code to make use of optional parameters:

class Dad {
virtual void method(int N=0) { print(”In class dad with value %d”, N);} // add optional (defaulted) parameter
virtual void otherMethod() { print(”Do something”);}
}

// Son stays the same

main(){
class Son son;
class Dad *ptr;

ptr = &son;
ptr->method(); // this now prints “In class dad with value 0″ !!!!!! No change to Son, no change to this line but the affect is different - ouch!
}

I didn’t write the compiler but what I figure is happening is that because the parameter is optional (defaulted) the code
ptr->method();
becomes
ptr->method(0);
And we are back to “Son doesn’t have a method called method that takes a parameter so I must want the one in Dad.”

Which just teaches us what we should have known already - sometimes you need to be very clever just to be clever.

Wow! I’ve bought a PC! You may think that’s the kind of thing I do a lot but I’ve been working from home (on and off) for 20 something years so initially having a PC at home (albeit a work one) was more than most people had. That first unit was very much “mine” - it shared home and work duties.

In 2000 and a bit I went back into an office so bought a decent PC for home. Having trawled the net for the cheapest I ordered it only to have the company go bust the next day. Fortunately I got the cash back as it was a credit card order and I went for safety and bought from the company I was working for. However, it came pretty much bare bones and I had to install my own memory as well as software. That PC (a P3) with various disk (60G), OS (dual booting 98 & XP) memory upgrades (maxed out at 256M) has staggered on until now. The lack of memory being the real issue.

I’ve built PC’s out of work cast offs for various family members and ended up keeping a laptop ebayed for the in-laws but beyond their eyesight and co-ordination to use. Unfortunately a dodgy power connection on the laptop (battery was dead from day one) meant you could lose your work at any time and as it was also maxed out with 256M of memory the chances of doing anything before it died were minimal.

So I’ve bought a new laptop. New, from a shop, with software installed, legal paid for software and everything - not just some old bit of kit I’ve reformatted and put a collection of freeware and borrowings on. It took it out the box, turned it on and it worked - spooky.

And where did this ageing techie go for his hardware? Having considered another ebay purchase, having price checked the company’s staff discounts and special offers, having perused the many el cheapo sites I’ve squirreled away over the years my arcane knowledge took me to….

..Tesco.

Yes, my local supermarket had a good basic laptop for not much over £300 (£329 but double points traded up gives me effectively another £25 off that and you can get a £10 off on line purchases). http://direct.tesco.com/q/R.207-0318.aspx is not quite what I’d have chosen given days to pore over specs but it was close enough to both the price and performance I had sketched out in my head and easy to get hold of and to take back if it was DOA that it was a no brainer in the end.

If you’d have told me 25 years ago I’d buy a laptop along with the weekly shop….

http://www.itpro.co.uk/623338/microsoft-calls-ie6-spoiled-milk

All I am hearing is we need “Strong and stable government”, the implication usually being only a majority party can provide this. On the contrary, an effective coalition would be far more stable than the “Punch and Judy politics” that I heard so much of before the election. I can understand that it may not be as strong, if strong means being able to make decisions without giving them sufficient consideration or wide based support, however, that is all to the good.

It is time our politicians grew up, stopped assuming they are right and everyone else is wrong and started reaching compromise and consensus the way the rest of us have to operate.

Well it’s a small and coincidental world but my company’s election for works council members finished yesterday and as I am yet to receive a ballot paper I have some fellow feeling with http://news.bbc.co.uk/1/hi/uk_politics/election_2010/england/8666457.stm

Mistakes organising a company ballot aren’t good but surely as a country we are capable of allowing our citizens (subjects?) a chance to use the vote they have?

It could all be done on line but would I trust it? The problem is computer cock-ups tend to be more major and anyway if it was a government IT scheme you can be sure that it would cost a fortune and wouldn’t be ready on time…