Published: Monday, September 25, 2000
StrCat.Catter - An Efficient String Concatenation Component
By Michael Balloni
I wrote this component - StrCat.Catter - because string concatenation in
Visual Basic (Script) has poor performance characteristics. I found that code like
this:
<%
Dim rs
Set rs = ExecuteSql("SELECT Username FROM Users")
Dim some_str
some_str = ""
do until rs.EOF
some_str = some_str & rs(0) & "<br>" & vbCrLf
rs.MoveNext
loop
Response.Write some_str
%>
|
performed very poorly. The code took a long time to execute, during which time the
processor was totally saturated. I found articles on MSDN stating that this type of
code was a bad idea, and I've heard that this type of concatenation results in run
times that are proportional to the square of the number of concatenations. There are
times when a solution based on passing strings - instead of passing function pointers
or function objects capable of outputting strings - is favorable. For example, let's
say I have a general routine that asks the user to verify their billing information before
they make a purchase, and this routine needs to output a summary of what the user is
buying. You might be tempted to say:
<%
' Output your purchase summary...
' ...then output your billing information verification system.
%>
|
but what if your billing information verification code needs to sprinkle HTML on boths
sides of the purchase summary. Then you're better off passing that purchase summary -
as a string - to the billing information verification code. You could put together some
sort of "object that outputs purchase summaries when this method is called" type of
system - and VBScript allows for this type of system - but let's keep things simple and
pretend we just want to pass in a string and we need efficient string concatenation.
Enter StrCat.Catter. "Catter" is a C++ COM component with a
very small interface. Here's typical usage of it:
<%
Dim strcat
Set strcat = Server.CreateObject("StrCat.Catter")
Dim rs
Set rs = ExecuteSql("SELECT Username FROM Users")
do until rs.EOF
strcat rs(0) & "<br>" & vbCrLf
rs.MoveNext
loop
Dim some_str
some_str = strcat.Dump
Set strcat = nothing
Response.Write some_str
%>
|
That's pretty simple, isn't it? By having the concatenation method be the default
method, you just say the Catter's name - in this case strcat - and it just
tacks on the string you give it. When you're ready to use the whole string, call
Dump and you've got it!
In Part 2 we'll look at the implementation of our
Catter class and performance tests.
Read Part 2
