I have one header file named to say january.h and one source file january.cpp. (Syntax is OK)
I am using code block.
I kept both file in a same folder.
Now when I open .cpp file from within IDE and try to compile then comiler generate message "undefined reference to ...."
Now I create one empty project and allocate files to respective source file folder and header file folder and then it compiles OK.
I think there may be linkage problem in first case .