Library guidelines

Thiago Macieira thiago at
Thu Mar 16 10:51:26 GMT 2006

Frerich Raabe wrote:
>Hm, I'm a bit surprised that this is the case. If you use
> visibility=hidden when defining KMyClass::Private, it still gets
> exported just like KMyClass?

On Unix I can confirm that it gets a hidden visibility, but I am not sure 
on Windows. Someone will have to test.

But I wouldn't be surprised if it inherited the visibility from the 

> I would have thought that to the linker 
> (who, if I understood all this correctly, is the one who strips symbols
> with hidden visibility [unlike with static symbols]) it doesn't make a
> difference whether a class is callied QuakPrivate or Quak::Private,
> it's going to be mangled anyway.

Right, but it's the compiler that tells the linker whether a symbol has 
default or hidden visibility.

>> However, it is preferred to use this practice if the alternative is
>> code that is of difficult readability and/or maintenance."
>You could also use one long string and an array of offsets:
>static const char stringData[] = {
>	"message1\0",
>	"message2\0",
>	0

You mean without the commas there and the final zero.

>static int stringDataOffsets[] = {
>	0,
>	9
>static const char *message( int no ) {
>	return stringData + stringDataOffsets[ no ];
>Then you don't have to relocate anything at all, and all data can
> probably (I'm not sure, but I'd guess so) be put in non-writeable
> (shareable) memory pages, yet you don't have a runtime cost as with
> QList<QByteArray> or something else. I think moc does something like
> that with Qt 4.x as well.

Yes, that's what moc does.

That's fine for generated code, but that's really hard to maintain in 
hand-written code. If you change one string, you have to update all 
offsets from there until the end.

That's a trade-off: either you get code readability or you get less 

Thiago Macieira  -  thiago (AT) - thiago (AT)
  thiago.macieira (AT)     Trolltech AS
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