How to generate a constexpr version string from three integers (or perhaps a git/SVN commit/rev. string)?

Question

Say I have

constexpr const std::uint8_t major = 1;
constexpr const std::uint8_t minor = 10;
constexpr const std::uint8_t bugfix = 0;

and I

Answer 1

Here is a C++11 solution. It uses class templates with char... parameter pack to simulate strings:

#include 
#include 

template 
struct String
{
    static constexpr char value[] = {symbols...};
};

template 
constexpr char String::value[];

template 
struct Concat;

template 
struct Concat, String>
{
    using type = String;
};

template 
struct Concatenate;

template 
struct Concatenate
{
    using type = typename Concat::type>::type;
};

template <>
struct Concatenate<>
{
    using type = String<>;
};

template 
struct NumberToString
{
    using type = typename Concat
        <
            typename std::conditional<(N >= 10), typename NumberToString::type, String<>>::type,
            String<'0' + N % 10>
        >::type;
};

template <>
struct NumberToString<0>
{
    using type = String<'0'>;
};

constexpr const std::uint8_t major = 1;
constexpr const std::uint8_t minor = 10;
constexpr const std::uint8_t bugfix = 0;

using VersionString = Concatenate
    <
        NumberToString::type,
        String<'.'>,
        NumberToString::type,
        String<'.'>,
        NumberToString::type
    >::type;

constexpr const char* version_string = VersionString::value;

int main()
{
    std::cout << version_string << std::endl;
}

See live example.