I always open the external file in code::blocks.
After I modified the file without saving it right now, and return to edit a cpp file, and then when I switch to edit the external file again, something wrong had happened.
Whatever I type in, there was no response. The file editor for the external file had no response. But when I save the file, I found that what I type in become effective.
It means that, when I modify a external file, and switch to edit other file, I have to save the external file which I modified just now so that I can edit it next time.
I found that this bug just happened in Ubuntu, including and not limited to Ubuntu 16.04, 18.10.
Lots of version of code::blocks have this bug, including and not limited to codeblocks 16.10, 17.12.