devxlogo

Faster string appending with Mid$ command

Faster string appending with Mid$ command

As you probably know, the “&” operator is rather slow, especially with long strings. When you have to repeatedly append chucks of characters to the same variable, you can speed up your code using a simple trick based on the Mid$ command. The idea is that you pre-allocate a buffer longenough to accomodate for the result of your operation. Here’s an example of this technique.

Suppose you want to create a string given by appending the first 10000integers, e.g. “1 2 3 4 5 6 7 … 9999 10000”. This is the easiest way to do so:

res = ""For i = 1 to 10000: res = res & Str(i): Next

The problem with the standard approach is that the res variable is reallocated 10000 times. This is a better way to reach the same result:

Dim res As StringDim i As LongDim index As Long' prepare a buffer long enoughres = Space(90000)' this points to where we want to insert the stringindex = 1' here we goFor i = 1 to 10000    substr = Str(i)    length = Len(substr)    ' stuff the string inside the result variable    Mid$(res, index, length) = substr    ' advance index    index = index + lengthNext' drop extra charsres = Left$(res, index - 1)

The standard code takes 2.2 seconds on my 333 MHz system computer, while the smart way takes only 0.08 seconds, so it’s 25+ times faster.

See also  Is Machine Learning Automating Creativity in Graphic Design?
devxblackblue

About Our Editorial Process

At DevX, we’re dedicated to tech entrepreneurship. Our team closely follows industry shifts, new products, AI breakthroughs, technology trends, and funding announcements. Articles undergo thorough editing to ensure accuracy and clarity, reflecting DevX’s style and supporting entrepreneurs in the tech sphere.

See our full editorial policy.

About Our Journalist