To create cooked user-defined literals, you should follow these steps:

1. Define your literals in a separate namespace to avoid name clashes.
2. Always prefix the user-defined suffix with an underscore (_).
3. Define a literal operator of the following form for cooked literals:

        T operator "" _suffix(unsigned long long int); 
        T operator "" _suffix(long double); 
        T operator "" _suffix(char); 
        T operator "" _suffix(wchar_t); 
        T operator "" _suffix(char16_t); 
        T operator "" _suffix(char32_t); 
        T operator "" _suffix(char const *, std::size_t); 
        T operator "" _suffix(wchar_t const *, std::size_t); 
        T operator "" _suffix(char16_t const *, std::size_t); 
        T operator "" _suffix(char32_t const *, std::size_t);

The following example creates a user-defined literal for specifying kilobytes:

    namespace compunits 
    { 
      constexpr size_t operator "" _KB(unsigned long long const size) 
      { 
        return static_cast<size_t>(size * 1024); 
      } 
    } 

    auto size{ 4_KB };         // size_t size = 4096; 

    using byte = unsigned char; 
    auto buffer = std::array<byte, 1_KB>{};