templates - c++ va_list function overload -

i have 2 function overloads:

void log(const char* format, ...); void log(const string& message); 

and want in case of call: log("hello"); string version called, or in other words first overload should called in case of 2 arguments or more.

i thought doing this:

template<typename t> void log(const char* format, t first, ...); 

but in case have trouble using va_list in code.

is there other solution might missing?

edit: thought checking size of va_list inside function, , redirecting in case of 0, far understood it's impossible size of va_list.

1. force type construction: log(std::string{"hello}). isn't seem want.

2. in either of functions, call other one.

   void log(const string& s)   {       log(s.c_str());       } 

   but it's not efficient because you'll have useless string object, although compiler may able inline call.

3. use variadic templates , sfinae:

   void log(const string&); auto log(const char *ptr, args&& ... args) ->       typename std::enable_if<sizeof...(args) != 0, void>::type  

   the second overload available in set of candidate functions if there're trailing arguments. showcase. in c++14, can use short-hand version of std::enable_if, std::enable_if_t, makes syntax clearer:

   auto log(const char *ptr, args&& ... args) -> std::enable_if_t<sizeof...(args) != 0, void> 

   you can still simplify in c++11 using

   template <bool b, typename t> using enable_if_t = typename std::enable_if<b, t>::type; 

if you're calling function accepts va_list (such printf) you're still able expand pack of parameters:

std::printf(ptr, args...); 

but not vice versa.