Question

I’m getting confused with my C++ class structure below:

A.h:
  class A{
};

A.cpp
//implementation for A
  void A::someMethod();

B.cpp:
#include "A.h"

B : public A{

//stuff for B
};
int main{
   B b();
   b.someMethod();
}

g++ A.cpp A.h –> compiles fine

g++ B.cpp –> undefined reference to main

Answer 1

You need to do:

g++ A.cpp -c
g++ B.cpp -c

To generate A.o and B.o (without -c g++ expects to link and produce a complete executable – and expects a main function, whereas -c specifies compile and assemble but do not link).

You can then link the two object files into an executable using:

g++ A.o B.o

Also: do not specify the header files on the command line. You need to specify them using #include directives in your cpp files and then the compiler will pull their contents in directly as the pre-processing stage of compiling each cpp. If you’re interested in the details of the stages of compilation for C++, Microsoft have detailed those for their compiler here.