I'm not sure if this is the right place to post this, if it isn't I apologize.

When I try to compile a single file with GCC (I'm using Code::Blocks as my IDE if that is relevant) it gives me a bunch of undefined reference errors. Well, of course they are undefined since I haven't linked anything yet, but why is GCC complaining at compiling time?
The problem is that when I try to link and compile the project in one go I don't get any errors. So what am I doing wrong here?

The references in question are from the GLEW library if that is relevant.

src\charrenderer.o:charrenderer.cpp|| undefined reference to `_imp____glewDeleteBuffers'|
src\charrenderer.o:charrenderer.cpp|| undefined reference to `_imp____glewDeleteBuffers'|
src\charrenderer.o:charrenderer.cpp|| undefined reference to `glEnableClientState@4'|
src\charrenderer.o:charrenderer.cpp|| undefined reference to `_imp____glewBindBuffer'|
src\charrenderer.o:charrenderer.cpp|| undefined reference to `glVertexPointer@16'|
src\charrenderer.o:charrenderer.cpp|| undefined reference to `_imp____glewBindBuffer'|
src\charrenderer.o:charrenderer.cpp|| undefined reference to `glDrawElements@16'|
src\charrenderer.o:charrenderer.cpp|| undefined reference to `glDisableClientState@4'|
src\charrenderer.o:charrenderer.cpp|| undefined reference to `glGetError@0'|
src\charrenderer.o:charrenderer.cpp|| undefined reference to `_imp____glewGenBuffers'|
src\charrenderer.o:charrenderer.cpp|| undefined reference to `_imp____glewBindBuffer'|
src\charrenderer.o:charrenderer.cpp|| undefined reference to `_imp____glewBufferData'|
src\charrenderer.o:charrenderer.cpp|| undefined reference to `_imp____glewGenBuffers'|
src\charrenderer.o:charrenderer.cpp|| undefined reference to `_imp____glewBindBuffer'|
src\charrenderer.o:charrenderer.cpp|| undefined reference to `_imp____glewBufferData'|
src\charrenderer.o:charrenderer.cpp|| undefined reference to `_imp____glewBindBuffer'|
src\charrenderer.o:charrenderer.cpp|| undefined reference to `_imp____glewBindBuffer'|
||=== Build finished: 17 errors, 0 warnings (0 minutes, 1 seconds) ===|

Here are all the errors I get.
Any help would be much appreciated, thank you in advance.