CppUG_UserDefinedLiterals.cpp

#include <iostream>
#include <chrono>

// used as conversion 
constexpr long double operator"" _m ( long double m ) {
    return m;
}

constexpr long double operator"" _km ( long double km ) {
    return km * 1000.0_m;
}

constexpr long double operator"" _nmi ( long double nmi ) {
    return nmi * 1852.0_m;
}

// used for side-effects
void operator"" _print ( const char* str ) {
    std::cout << str << '\n';
}

int main() {
    const double distance_sea = 150.0_nmi;
    const double distance = distance_sea / 1.0_km;
    std::cout << std::fixed << distance_sea  << "m\n";
    std::cout << std::fixed << distance  << "km\n";
    0x123ABC_print;
#if __cplusplus > 201103L
    // With C++14 some literal operators are defined in the standard library 
    using namespace std::chrono_literals;
    auto d1 = 250ns;
    std::chrono::nanoseconds d2 = 1us;
    std::cout << "250ns = " << d1.count() << " nanoseconds\n"
              << "1us = " << d2.count() << " nanoseconds\n";
#endif    
}