Wednesday, March 3, 2010

OOP344: Logic problem

Part of my contribution to this first programming project was to code the section of the function that would actually let the user insert characters into a line. (Project specs here. The function I'm working on with everyone is bio_edit()). On and off during the week of the due date, I had successes, but the last hurdle stumped me. At some point in time, everything was working perfectly--it's simple logic--and then I just had to re-do someone else's code, and everything with regards to insertMode stopped working.

Someone suggested using memmove when shifting the string, but since I was (and still am) afraid to use a function I hadn't used before, I decided to stick to a for-loop. It didn't work as well as I thought. I coded it so that when inserting characters, everything from the end of the string to the current cursor position was shifted to the right, and the character typed would be inserted in the current cursor position (*curpos). However, the characters being shifted included those beyond *curpos, and any letters I typed were basically overwritten by whatever was to the left of the cursor.

I isolated this section still got the same results. My code looked like this:
Then I got it fixed with this:

Line 645 now takes into account *offset where it didn't use to (line 508 in the first screenshot). The really bad part about trying to debug this was programmer failure--I kept forgetting the fact that *curpos is related only to length of the editing field and not the str being edited. *offset + *curpos is the index of any character in str. Whenever I tried doing a walkthrough, everything made sense. At some point, I stared at my long enough to realize it. Massive failure.

Though the project has been submitted, I'm still going to attempt using memmove to reduce the number of lines. (That is, if playing Prototype doesn't get in the way, haha.)

No comments:

Post a Comment