Well, i have been customizing my WordPress a lot to produce something like the food directory or blogshopping tool which required a lot of hack on to WordPress to make everything work perfectly. Recently i have upgraded my WordPress to the latest version 3.0.1. Everything seems fine until one day i decided to enhance my site. Upon activting my WordPress plugin, an error message occurs stating "The plugin generated 3 characters of unexpected output during activation. If you notice “headers already sent” messages, problems with syndication feeds or other issues, try deactivating or removing this plugin.". Although the plugin successfully activated, it seems like there are some problem with the plugin that is causing this. I search high and low for it but couldn't seems to detect any header being sent explicitly without my knowledge. To make matter worst, this caused all my timthumb (image of the fly) script to malfunction which caused ALL my images to break. Hence, none of the images generated by timthumb were generated on the website. This is disaster!!! Why is my header being sent when there is NOTHING in my code that is sending it?!!! (panic)
I went to alert my hosting company (hostgator) about this and tried to resolved this on the server level as my test environment which is another host were functioning perfectly without causing me a single problem! However, they couldn't find any cause on their server side that may caused this problem and direct me back to the application problem and asked me to check my code. Puzzled by all the mystery that is happening on my test and live environment. I decided to look further into what could have happened. And here are some of the things that i found but doesn't happen to me.
Extra whitespace / Character
Extra whitespace or character before the tag will caused this to happen. This is a comment mistakes made by many new php developers. But in my case, this wasn't the problem.
Soon, i found out my mistake. Apparently, my test environment server setting allows Unicode encoded file type to be read normally. However, the one on Hostgator only allows ANSCII to be read. Hence, all the Unicode encoded files were the culprits that is causing all this problems. It seems like the php setting made on the server can caused this to happen as the file type unknown to the php parser seems to bypassed the php output buffer and sent out the plaintext mime type before everything else which caused my timthumb to not work properly (since image sent in jpg mime instead of plaintext). This might be the reason why WordPress is giving you a message of "The plugin generated 3 characters of unexpected output during activation. If you notice “headers already sent” messages, problems with syndication feeds or other issues, try deactivating or removing this plugin." when you try to activate the plugin. It can also be caused by other plugins builder who are unaware that this might happen as their environment works perfectly and yours doesn't. Oh, the reason why anyone would want to change the encoding from ASCII to other form of encoding can be due to special character or other languages writing that ASCII doesn't support. Hence, changing the file encoding types allows php to display out the correct message. (WordPress is multilingual, this should happen more often than you think :)). Hope it helps 🙂