[Qgis-user] New Labeling: conditional labels

[Andreas Neumann]

 Hi Giuseppe,

 Thanks for the further clarifications. With your additional hints I now 
 fully understand how the substr function works and why we use *-1 here.

 Andreas

 On Thu, 29 Dec 2011 15:35:20 +0100, Giuseppe Sucameli wrote:
> On Thu, Dec 29, 2011 at 2:18 PM, Giuseppe Sucameli
> <sucameli at faunalia.it> wrote:
>> On Thu, Dec 29, 2011 at 11:25 AM, Andreas Neumann 
>> <a.neumann at carto.net> wrote:
>>>What I do not understand is why I need the *-1 (multiplier).
>>
>> I usually use -1 in python to get the entire string
> ...
>> The function help says:
>> substr(string,startpos,length)
>> so we need to use the string length, but also the startpos values
>> starts from 1, not 0... (and the help doesn't help to understand 
>> it).
>
> looking at the code, here's what the susbstr function calls:
> string.mid( startpos -1, length )
>
> Now looking at QString.mid() [1] I can confirm that
> using the susbstr function:
> startpos starts from position 1 (not 0) and
> if length is -1 then all chararcters available from startpos are
> returned.
>
> So you can use either substr(id, 1, (id > 0)*-1) or
> substr(id, 1, (id > 0)*length(id)), both are valid and working 
> syntax.
>
> I think we should improve also the help to add those informations.
>
> Regards.
>
> [1]
> 
> http://developer.qt.nokia.com/doc/qt-4.7/qstring.html#id-71632fd3-c671-4ae0-9791-bce0d200b511

-- 
 --
 Andreas Neumann
 Böschacherstrasse 10A
 8624 Grüt (Gossau ZH)
 Switzerland