Initializing a static char based on template parameter

问题

I want to do something like this :

template<typename T>
const char * toStr(T num)
{
    thread_local static char rc[someval*sizeof(T)] str = "0x000...\0"; // num of zeros depends on size of T
    // do something with str
    return str;
}

I'm guessing there's some template metaprogramming I'd have to do but I'm not sure where to start.

Edit:

I found a related question here: How to concatenate a const char* in compile time

But I don't want the dependency on boost.

回答1:

Not sure to understand what do you want but... if you want that the str initial value is created compile time and if you accept that toStr() call and helper function (toStrH() in the following example) a C++14 example follows

#include <utility>

template <typename T, std::size_t ... I>
const char * toStrH (T const & num, std::index_sequence<I...> const &)
 {
   static char str[3U+sizeof...(I)] { '0', 'x', ((void)I, '0')..., '\0' };

   // do someting with num

   return str;
 }

template <typename T>
const char * toStr (T const & num)
 { return toStrH(num, std::make_index_sequence<(sizeof(T)<<1U)>{}); }

int main()
 {
   toStr(123);
 }

If you need a C++11 solution, substitute std::make_index_sequence() and std::index_sequence isn't difficult.

来源：https://stackoverflow.com/questions/42450025/initializing-a-static-char-based-on-template-parameter