Am Dienstag, den 21.06.2005, 19:46 +0200 schrieb Michael Van Canneyt:
>
> On Tue, 21 Jun 2005, Marc Santhoff wrote:
>
> > Hi,
> >
> > in an application of mine occurs a lot of string separation and
> > re-concatenation. Since it is using masses of ANSI strings this is some
> > performance problem.
> >
> > The strings get stored and loaded from TStringList's and concatenated
> > by simply using '+' and separated with the function copy().
> >
> > What I'd like to know is: What's are fastest ways of handling ANSI
> > strings?
>
> It's hard to say in general; You would have to supply some example code.
>
> if you're doing things like
> For I:=X to Y do
> S:=S+L[i]; // S string, L list.
Somewhat similar to that:
if (sl[4] <> '') then
if ((sl[4][1] = '"') AND (sl[4][length(sl[4])] = '"'))
then BaseColor := copy(sl[4],2,length(sl[4])-2) else
BaseColor :=
sl[4];
where BaseColor is a field of a class-type object, sl is a TStringList.
I have to look for double quotes here and cut them out if necessary.
Sequences like this are heavily used in loading CSV files. This takes
rather long on a 'small' cpu (Geode 300MHz).
> then
> It might be better to do
>
> Len:=0;
> For I:=X to Y do
> Inc(Len,Length(L[i])); // S string, L list.
> SetLength(S,Len);
> P:=1;
> For I:=X to Y do
> begin
> T:=L[i];
> Len:=Length(T);
> Move(T[1],S[P],Len);
> inc(P,Len)
> end;
>
> This will avoid a lot of calls to uniquestring, get/setlength etc.
Another snippet esecially for concatenation is this:
result := IntToStr(ID) + SEP +
IntToStr(ID_Customer) + SEP +
QT + Treatment + QT + SEP +
DateToStr(Date) + SEP +
QT + BaseColor + QT + SEP +
... and so on for approx. 15 fields
I think I'll try your technique here ...
> Also, keep in mind that getting the I-th string from a list is an expensive
> operation.
>
> So it is better to do
> T:=L[i];
> S:=Copy(T,X,Length(T)-X);
> than to do
> S:=Copy(L[i],X,Length(L[i])-X);
>
> The first option will call GetString only once, the second will call it twice.
This will help me, I'm sure. :)
Thank you so far,
Marc
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