The log was the same as the first post. However I just solved my problem.
So, I was quite curious what the .cbp file looks like inside, which I then found out to be in an XML format. Looking through the tags, I found the tag '<Unit filename="main.c">'. I tinkered it by replacing it with "jsoncpp.cpp".
At first, I thought it didn't do anything when I try to rebuild it.
Then I thought of relaunching Code::Blocks and open the project file afterwards to load up from the modded .cbp file.
And so I did, then opened the "jsoncpp.cpp" file, pressed F9, and it is fixed.