Personal data on software defects

Recently, I spent a week at a simulator facility supporting checkout of software changes. During the week, I created several prototype changes for new features. I had a number of issues, and decided to share some data on those issues.

1. Editing problems
I was asked to swap a parameter used in a calculation for another parameter. I was editing source code in a Subversion branch checkout. However, one of the files I had opened was from a trunk checkout of the same software baseline. This file had the main declaration of the new parameter. As a result, I was getting an “undefined parameter” linking error. I thought I had confirmed that all of the files I was using was in the branch checkout directory, but that was not the case. I had to get two of my peers to take a look at what I had done, one of them was able to successfully compile the code changes. That gave me the idea to recheck the location of the files, and I then saw the problem.

2. Compile errors – part 1
My next prototype was a significant modification of two functions. I had a set of redlined requirements, and decided to do a pair programming exercise with the flight control engineer who developed the requirement changes. We reviewed the code changes as we went, then started compiling and removing errors. Here is what I had:
a. Forgot to update function prototypes in include file
b. Two LOC had semicolons when they should have had no semicolons (function initial statements)
c. One incorrect variable declaration
It took about 5 minutes to correct those problems.

3. Compile errors – part 2
I got a set of draft requirements for a new algorithm from an engineer. The requirements were in a Word document, and included some pseudocode and actual code snippets. I created the initial prototype by myself, then reviewed it with the engineer. After our review, I then started compiling and removing errors. I cannot remember the early errors, but there was one that persisted. The compiler was telling me that there was a problem with a character on two line, but did not directly identify the character. The problem was when I copy/pasted the code snippets, the minus sign in two equations was not a dash, but some other character. I deleted that text and retyped the minus signs, and that corrected the final problem.

Summary
1. When in a hurry, take time to review your changes.
2. When copy/pasting from a Word document, be sure to check equation text.
3. Pair programming can be a useful development method.