It's Turing complete because it could simulate a Turing machine, not because of metaprogramming. The language brainfuck is Turing complete, for example.
Checking if a Brainfuck program is well formed (i.e. can be run) is a linear time operation. In C++ this can take forever. They have different complexities.
The original comment was about Turing completeness, and it was defined incorrectly. I was giving an example of a dead-simple language that was Turing complete, because the claim was that metaprogramming made C++ Turing complete.
The claim wasn’t that C++ is Turing complete, that’s trivially true. The claim was that C++’s grammar is Turing complete. I don’t know if that’s exactly the right way to phrase it, but C++’s template expansion stuff is Turing complete.
Yes, but it is the difference to other programming languages.
In C you cannot encode a Turing machine that is executed by the compiler at compile time. In Brainfuck you cannot encode a Turing machine that is executed by the compiler at compile time. In C++ you can encode a Turing machine that is executed by the compiler at compile time.
No. You would need the ability to write unbounded loops or unbounded recursion. You don't have that with the C preprocessor.
Yes, you can do a lot with the C preprocessor. You can also do a lot in languages that only have bounded loops and are therefore not Turing complete. You can either express nonterminating computations (Turing completeness), or you can't (still powerful, but dramatically less poweful). This question is binary. There is no fuzziness, there is no approximation, there is no "quite close".
