C++ Templates: Convincing self against code bloat

Question

I have heard about code bloats in context of C++ templates. I know that is not the case with modern C++ compilers. But, I want to construct an example and convince myself.

Answer 1

In this specific case, you'll find that g++ will tend to inline the accessor if you have any sort of optimization on. That right there is some minor code bloat, though it's debatable if the overhead of the call would be any less.

However, one easy way to verify what's getting compiled is with the nm tool. If I compile your code with a simple main() to exercise ArrayX::data() and ArrayY::data() and then compile it with -O0 to turn off inlining, I can run nm -C to see the symbols in the executable:

% nm -C test
0804a040 B ArrayX
0804a1e0 B ArrayY
08049f08 d _DYNAMIC
08049ff4 d _GLOBAL_OFFSET_TABLE_
0804858c R _IO_stdin_used
         w _Jv_RegisterClasses
080484c4 W Array::data()
08049ef8 d __CTOR_END__
08049ef4 d __CTOR_LIST__
08049f00 D __DTOR_END__
...

You'll see that the Array::data() symbol only occurs once in the final executable even though the object file for each of the two translation units contains it's own copy. (The nm tool also works on object files. You can use it to check that x.o and y.o each has a copy of Array::data().)

If nm doesn't provide enough detail, you might also have a look at the objdump tool. It's a lot like nm, but with debugging symbols turned on, it can even show you things like a disassembly of the output executable with intermixed source lines.