C++: Compiler and Linker functionality

Question

I want to understand exactly which part of a program compiler looks at and which the linker looks at. So I wrote the following code:

#include          


        

Answer 1

The linker is there to link in code defined (possibly) in external modules - libraries or object files you will use together with this particular source file to generate the complete executable. So, if you have a declaration but no definition, your code will compile because the compiler knows the linker might find the missing code somewhere else and make it work. Therefore, in this case you will get an error from the linker, not the compiler.

If, on the other hand, there's a syntax error in your code, the compiler can't even compile and you will get an error at this stage. Macros and templates may behave a bit differently yet, not causing errors if they are not used (templates are about as much as macros with a somewhat nicer interface), but it also depends on the error's gravity. If you mess up so much that the compiler can't figure it out where the templated/macro code ends and regular code starts, it won't be able to compile.

With regular code, the compiler must compile even dead code (code not referenced in your source file) because someone might want to use that code from another source file, by linking your .o file to his code. Therefore non-templated/macro code must be syntactically correct even if it is not directly used in the same source file.