Worst example of you duplicating existing functionality?

Question

I've certainly done this : written a load of code to do some operation, then discovered that the language already had that functionality built in. An early case i remember is writing a function to reverse a string in VB6, then stumbling across StrReverse a week later. What's your worst example of this?

Answer 1

Creating a function in VB6 to create a string with a number of spaces.
I later found that I could simply do:

Dim str As String
str = String(10)

Answer 2

We once tried to create a method to shuffle a Collection in Java :)

EDIT: corrected "sort" to "shuffle"

Answer 3

Copying arrays, only to later find that you have System.arraycopy().

Answer 4

One of my co-worker once tried to write a full-featured XML parser in c# ...

Answer 5

I once tried to write HTML editor in jscript as my employer did not want to buy one in or use an open source one.

Answer 6

In one inspired period during my first programming job I decided it would be a good idea to write a thread pool to deal with a number of items of work in parallel in C#. Armed with a list of jobs to process and a maximum number of threads I could use I set to work.

My downfall came when I decided that keeping the thread pool going with while (true) and no sleep was a good idea. A sentiment not shared by my fellow developers, especially since I ran the service on our main database server. I think it took two minutes before someone spotted things 'had got a little slow' on the box.

Needless to say I now think of 'the threadpool incident' and look around for things someone else has written before deciding I need to reinvent the wheel.

Answer 7

I once implemented several sorting algorithms in Java only to have my boss tell me about Java's sorting classes.

Answer 8

A couple of jobs ago a co-worker didn't trust SQL's JOIN so he set about writing one himself...