Question

I am using the Codeblock IDE with MingW, I have an ongoing problem
with the following types of errors. (File || Message)

obj\CEntity.o(.text+0x71a) || In function `ZN7CEntity6OnMoveEff':

OR

obj\CArea.o(.bss+0x0) || In function `ZNSt6vectorI5CTileSaIS0_EEaSERKS2_':
obj\CApp_OnCleanup.o(.bss+0x0):C:\DevCpp\bin\..\lib\gcc\mingw32\3.4.2\..\..\..\..\include\c++\3.4.2\bits\vector.tcc || first defined here

Note that it gives the location as some sort of obj file so I cannot
see where it is in my code.

My C++ is improving a lot but I am still not very good understanding
how the compilers work and I cannot figure out what might be causing
the problem or how to go about solving issues like this. Unlike a code
problem it is really hard to google because the names have just been
scrambled.

Hopefully someone can help because it is holding me back and I just cannot find
or figure out a fix!

(I decided not to post my code because it is many interlinked files and I do not
know where the error is but I am trying to follow the tutorials on http://www.sdltutorials.com/sdl-tutorial-basics. The first few I can get to work
but then the later ones always seem to fail. It is obviously something I am doing wrong
because when I use the sample it works.)

Answer 1

Many GCC distributions (such as the MinGW distros I use) come with a utility names c++filt which will turn a C++ mangled name into something closer to the source code declaration (I think your error messages left out some underscores):

C:\temp>c++filt __ZN7CEntity6OnMoveEff
CEntity::OnMove(float, float)

MSVC comes with a similar utility: undname

However, you may want to update the MinGW you’re using. I get nice, demangled names directly in the error output going back to MinGW 3.4.5 (similarly for MSVC going back to VC++6):

class CEntity {
    public:
        void OnMove(float, float);
};

int main()
{
    CEntity ent;
    ent.OnMove(1., 2.);
}

Compiled with MinGW 3.4.5:

C:\temp>g++ -o test.exe test.cpp
C:\...\ccwlXEih.o:test.cpp:(.text+0x43): undefined reference to `CEntity::OnMove(float, float)'