I know C++ template metaprogramming is Turing-complete. Does the same thing hold for preprocessor metaprogramming?
I know C++ template metaprogramming is Turing-complete. Does the same thing hold for preprocessor
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I know C++ template metaprogramming is Turing-complete. Does the same thing hold for preprocessor metaprogramming?
No. The C++ preprocessor does not allow for unlimited state. You only have a finite number of on/off states, plus a include stack. This makes it a push-down automaton, not a turing machine (this ignores also the fact that preprocessor recursion is limited – but so is template recursion).
However, if you bend your definitions a bit, this is possible by invoking the preprocessor multiple times – by allowing the preprocessor to generate a program which re-invokes the preprocessor, and looping externally, it is indeed possible to make a turing machine with the preprocessor. The linked example uses C, but it should be adaptable into C++ easily enough.