How can codeblocks go from finding header files to not being able to find them, when none of the source code has changed?

Question

Why would a project be able to compile and find the necessary header files, and then I add a line that it cannot find, it does not compile, I remove that line (the code now looks exactly as it did when it compiled the first time) and now suddenly it cannot find the header files that it could find only a moment ago? I did not change any of the file structures, absolutely nothing changed other than adding a line, removing it, and everything is broken.

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I have followed every instruction in the Ogre3D tutorials up to building the first tutorial. Everything works perfectly fine and the first tutorial compiles and runs. So I decide to see if I can get a different tutorial to do the same thing, but alas the compiler throws an error: No such file or directory when looking at the line #include "Ogre.h". So I go back to the first tutorial's framework, I include all the lines and it still compiles as expected and then I decide to remove all of the source files and everything, and I take the very first include directive from the BaseApplication.h, the line is #include <OgreCamera.h>, and I put this lonely line in a single file main.cpp and attempt to compile this 1 line program. The same error occurs, it cannot find OgreCamera.h! What??

So what is so special that the tutorial framework compiles but when I try to do basically the exact same thing it throws a fit.

Update

Even stranger things are happening now... I added the line #include "Ogre.h" to the tutorial framework's BaseApplication.h file, it cannot find Ogre.h. So I remove that line and try to compile the program (which compiled not more than 10 seconds ago) and now it no longer can find OgreCamera.h! But it has literally not changed at all in any shape or form that I can tell. This is confusion of maddening proportions now!

Answer 1

I believe I know what I have done to myself here.. and recreated the problem

I followed the tutorials and setting up an application to the letter, and was having some other problem when I decided to copy the entire project I had already made doing the tedious setup things necessary. Without realizing that copying the entire project by simply copy-pasting the directory does not carry the tedious setup things necessary. And so, probably without paying attention to the "Target is up to date." build message, assuming it compiled I changed the files, it did not compile as expected, and then changed them back to their original state, and it still did not compile because they were no longer up to date.

I am going to remember this... for a long time.

Answer 2

Where the header files are resolved from is not defined in the code itself, but in the IDE and/or code::blocks project preferences. This tutorial is more relevant for setting up the search directories for Ogre header files.

If it was working a short while ago and not now, I would suspect you have probably made a simple mistake like switching from Debug to Release, having only configured the search directories for Debug build in the project properties. (Clicking build options defaults to selecting Debug rather than all configurations). Try to re-add the Ogre directories in both Debug and Release builds.

Code::Blocks also lets you add search directories globally for the IDE, in the compiler and debugger settings for commonly used libraries. You can also create a global variable for the Ogre SDK location to make it simpler to add to each new project. (#ogre.include), rather than adding the full/relative path.