I found a use of variadic templates in C++. This is constexpr max function that finds the max element in the list of arguments at compile time. Very strange that the standard library doesn't have it.
#include <iostream>
template<typename T>
constexpr T max(T a) {
return a;
}
template<typename T, typename... Rest>
constexpr T max(T a, Rest... rest) {
T b = max(rest...);
return a < b ? b : a;
}
int main(int argc, char const *argv[])
{
constexpr auto max_value_1 = max(1,2,3,4,9);
std::cout << max_value_1 << std::endl;
std::cout << max(9,1,2,3,4) << std::endl;
std::cout << max(1,9,2,3,4) << std::endl;
return 0;
}What I find strange is that variadic templates are not similar to variadic functions in C. I wanted to rewrite a C example with templates, but cannot figure this out. So here is just a C example.
#include <cstdarg>
#include <iostream>
enum class Hint {
COOL_ONE,
COOL_TWO,
COOL_THREE,
};
void cool_function(Hint hint, ...) {
va_list ap;
va_start(ap, hint);
switch (hint) {
case Hint::COOL_ONE:
{
unsigned int x = va_arg(ap, unsigned int);
std::cout << "COOL ONE: " << x << std::endl;
break;
}
case Hint::COOL_TWO:
{
double x = va_arg(ap, double);
double y = va_arg(ap, double);
std::cout << "COOL TWO: " << x << ", " << y << std::endl;
break;
}
case Hint::COOL_THREE:
{
char* c_string = va_arg(ap, char*);
size_t size = va_arg(ap, size_t);
std::cout << "COOL THREE: " << c_string << std::endl;
break;
}
default:
std::cout << "Impossible!" << std::endl;
break;
}
va_end(ap);
}
int main(int argc, char const *argv[])
{
cool_function(Hint::COOL_ONE, 42);
cool_function(Hint::COOL_TWO, 1.23, 4.56);
const char* test_string = "array of data";
cool_function(Hint::COOL_THREE, test_string, sizeof test_string);
return 0;
}As usual all code for your experiments and slides are in cpp-skill repository.