String vs. StringBuilder

BSkelding · June 29th, 2004, 09:59 AM

Which method is more efficient when adding repeated values to create one long string? Is it better to just concatenate on a string object, str1 = "Hello" & "There" & "Bob" or would using the StringBuilders append option be more effecient in code -
strBuilder.append("Hello")
strBuilder.append("There")
strBuilder.append("Bob")

Right now I'm trying to performance tune an application and it seems that these types of statements are taking up quite a bit of time. I'm pulling values from a database using a ODBC data reader and trying to create one long string record.

The way it's set up now I'm using a For-Next loop to iterate through all the fields returned by the datareader and then use a string builder to append the information. A sample of the code is below.

For intFieldCounter = 0 to (drPrev.FieldCount-1)
strRecord.append(drPrev(intfieldcounter))
Next

planoie · June 29th, 2004, 10:55 AM

Use the StringBuilder. It is optimized for building strings. Concatenation is slow as you have found.

A very useful method on the StringBuilder is the AppendFormat() method. String also has something similar (String.Format()). You can use this to append strings that are made of hard coded strings and variable values:

strName = "Peter"
strBuilder.AppendFormat("Hello, my name is {0}", strName)

BSkelding · June 30th, 2004, 07:31 AM

Okay, that's what I figured but it doens't hurt to check. One thing you mentioned in your reply; I've seen it in other examples and books as well is the use of {}. What does this do?

strBuilder.AppendFormat("Hello, my name is {0}", strName) Does the 0 correspond to anything in particular? I've wondered about it but never thought to ask what it does.

planoie · June 30th, 2004, 08:05 AM

The {n} refers to a format replacement token:

Code:

String.Format("{2} {1} {0}." , "Peter", "my name is", "Hello")
                ^   ^   ^      |_____|  |__________|  |_____|
                |   |   |_________/          |           |
                |   |________________________/           |
                |________________________________________/

The format methods (String.Format, StringBuilder.AppendFormat) take 1, 2 or 3 "Object" arguments, or an array of objects. You can use more than three replacement tokens with the overload that accepts an array. The tokens can be anywhere in the format string, and can occur multiple times. The token doesn't have to be in the string, but if there is a token in the string, there must be an accompanying object (either in the 1-3 argument list, or in the array).

Peter
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Work smarter, not harder