/dev/krzaq – Page 3

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

2014-10-272016-07-08 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.

Code Doodles #2 – the quirky switch

2014-02-062016-06-20 krzaq Leave a comment

According to grammar rules defined by the C++ standard (and C as well) the following code is valid:

switch(i) i++;

Stop assigning string literals to char* already!

2014-01-222020-02-19 krzaq 8 Comments

Every now and then I see people writing C++ code containing heresy in the vein of the following:

char * foo = "bar";

This is no more legal C++ than

const int qux = 42;
int * quux = &qux;

It is not undefined, unspecified or implementation defined! It is simply illegal

Code Doodles #1 – this code is legit… again

2014-01-102016-06-20 krzaq 1 Comment

The following is a legit, albeit a little obscure, C89 program. It is also a legit C++11 (and above) program.

int main(void)
{
	auto a = 42;
	return 0;
}

Readable function pointers

2013-12-272016-06-20 krzaq Leave a comment

Consider the following declaration

char*(*(*foo)(int(*)(char*,char*)))[]

It’s artificial (generated with the ever-helpful geordi bot), although I’m sure that if you looked hard enough, a similar one would appear somewhere in the wild. In the above case, foo is a pointer to function taking pointer to function taking char* and char* and returning int returning pointer to array of char*. I think that even seasoned C and C++ programmers will agree that this is quite confusing at first glance. Or second. And third. Especially for people less versed in “C gibberish”, as cdecl.org aptly calls it.