[Lazarus] UTF8String and UTF8Delete

[Jürgen Hestermann]

Am 2015-12-12 um 18:02 schrieb Sven Barth:
> On 12.12.2015 17:37, Jürgen Hestermann wrote:
>> Is it correct that now every ansistring has a static code page
>> and a dynamic code page (as mentioned in
>> http://wiki.freepascal.org/FPC_Unicode_support)?
>
> Yes.
>
>>
>> Is it correct that each ansistring type can store strings with any
>> encoding (dynamic code page) but there is a "genuine" (static) code
>> page which is preferred (in cases a target encoding needs to be chosen)?
>
> Yes.
>
>> What is the difference between
>>
>> UTF8String = type ansistring(cp_UTF8);
>>
>> and
>>
>> String = type ansistring(cp_ACP);
>> when cp_ACP=cp_UTF8?
>
> CP_ACP is *never* CP_UTF8. It is *always* CP_ACP. So these two will *always* be different types. However the specific codepage that CP_ACP refers to is determined at runtime and that can indeed be CP_UTF8.
>
>>
>> Both would have the same static code page (UTF-8) but may contain
>> a different encoding at run time. So why can't I use an UTF8String
>> in the same way as a String type as parameter?
>> Why are they not assignment compatible?
>
> They are assignment compatible (all AnsiStrings are) and the compiler will insert a code page conversion if necessary (if CP_ACP refers to CP_UTF8 and if one of the two strings is CP_ACP the other CP_UTF8 then the conversion routine won't do a code page conversion of course). However since they are different types you can't simply pass a AnsiString(CP_UTF8) to a var parameter of type AnsiString(CP_ACP).
>
Thanks for your answers.
At least some of my questions are answered now.
The wikis are not clear about it.
Especially, the role of CP_ACP is not clearly documented.