Category: Programming

An erase/remove idiom gotcha

krzaq 17 Comments

I was investigating a crash in my application recently. Despite working in the production environment, I was able to launch the debug version in a debugger (yay). Soon enough, I got a promising SIGSEGV in the expression implementing the erase-remove idiom:

vec.erase(std::remove_if(vec.begin(), vec.end(),
          [&orig](auto const& msg){
    return orig.id == msg.id;
}));

Can you spot the bug already?

Code doodles #3 – significant parentheses, C++14 style

krzaq 2 Comments

Hello, everyone. It has been a while since my last post.

While watching CppCon 2014 I found this little gem being described by Scott Meyers.

Consider the following code:

decltype(auto) foo()
{
	static int Foo;
	return Foo;
}
 
decltype(auto) bar()
{
	static int Bar;
	return (Bar);
}
 
int main()
{
	decltype(auto) a = foo();
	decltype(auto) b = bar();
	a++;
	b++;
	cout << foo() << ", " << bar() << endl;
}

Would you expect this to print 0, 0? Well, not so fast. decltype(auto) is just a nicer syntax for decltype(name), where name is “unparenthesized id-expression or an unparenthesized class member access”, as described here. Therefore it follows the same rules.

That’s another corner case to remember, but I guess it could also make a nifty party trick, if one can find the right party.