repeat.cpp

#include <iostream>
using namespace std;
template<int N, char C, char... Cs> struct repeatImpl : repeatImpl<N-1, C, C, Cs...> {};
template<char C, char... Cs> struct repeatImpl<0, C, Cs...> {
    static constexpr char cs[] = {Cs..., '\0'};
};
template<char C, char... Cs> constexpr char repeatImpl<0, C, Cs...>::cs[];

template<int N, char C> const char (& repeat())[N+1] {
    return repeatImpl<N, C>::cs;
}

int main (int argc, char const *argv[])
{
    cout << "str: " << repeat<5, 'x'>() << endl;
    return 0;
}