Is it possible to generate a string at compile time?

Question

In the following example I use snprintf inside a template function to create a string that contains the value of the template parameter N. I would like to know if there is a way to generate this string at compile time instead.

template <unsigned N>
void test()
{
    char str[8];
    snprintf(str, 8, "{%d}", N);
}

Why cant it happen at run time? Also, you might want to look at how C++ templating works (its all compile time based). — David says Reinstate Monica, Jul 04 '14 at 04:18
Exact duplicate of [C++ convert integer to string at compile time](http://stackoverflow.com/questions/6713420/c-convert-integer-to-string-at-compile-time) — metacubed, Jul 04 '14 at 04:19
Whatever it's worth at this point, http://coliru.stacked-crooked.com/a/b5c4c0c3b63b0c1b — chris, Jul 04 '14 at 04:21
@Dgrin91 It totally could happen at run-time, but it would be cool if it didn't have to. — Chris_F, Jul 04 '14 at 04:35
@metacubed It's not really an exact duplicate. I'm looking a string that contains more than just the number. Look at the code and see the format string. `"{%d}"` not `"%d"`. — Chris_F, Jul 04 '14 at 04:40
@Chris_F the linked question describes a macro - you can put any extra characters in there as per your needs. Even the scenario of the question (a template parameter) is the same. I could change my comment to "almost duplicate" if you like... :) — metacubed, Jul 04 '14 at 04:50

score 5 · Accepted Answer · edited May 23 '17 at 10:26

After a bit more digging around I came across this on SO: https://stackoverflow.com/a/24000041/897778

Adapted for my use case I get:

namespace detail
{
    template<unsigned... digits>
    struct to_chars { static const char value[]; };

    template<unsigned... digits>
    const char to_chars<digits...>::value[] = {'{', ('0' + digits)..., '}' , 0};

    template<unsigned rem, unsigned... digits>
    struct explode : explode<rem / 10, rem % 10, digits...> {};

    template<unsigned... digits>
    struct explode<0, digits...> : to_chars<digits...> {};
}

template<unsigned num>
struct num_to_string : detail::explode<num / 10, num % 10>
{};

template <unsigned N>
void test()
{
    const char* str = num_to_string<N>::value;
}

boost::mpl was also suggested, but this code seems simpler.

Is it possible to generate a string at compile time?

1 Answers1

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