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Embedded Programming with Modern C++

- Examples

In this lesson, we will look at some examples of variadic templates.

We'll cover the following...

Example 1 #

C++
// templateVariadicTemplates.cpp
#include <iostream>
template <typename... Args>
int printSize(Args... args){
  return sizeof ...(args);
}
template<int ...>
struct Mult;
template<>
struct Mult<>{
  static const int value= 1;
};
template<int i, int ... tail>
struct Mult<i, tail ...>{
  static const int value= i * Mult<tail ...>::value;
};
int main(){
  std::cout << std::endl;
  std::cout << "printSize(): " << printSize() << std::endl;
  std::cout << "printSize(template,2011,true): " << printSize("template",2011,true) << std::endl;
  std::cout << "printSize(1, 2.5, 4, 5, 10): " <<  printSize(1, 2.5, 4, 5, 10) << std::endl;
  std::cout << std::endl;
  std::cout << "Mult<10>::value: " << Mult<10>::value << std::endl;
  std::cout << "Mult<10,10,10>::value: " << Mult<10,10,10>::value << std::endl;
  std::cout << "Mult<1,2,3,4,5>::value: " << Mult<1,2,3,4,5>::value << std::endl;
  std::cout << std::endl;
}

Explanation #

  • In the above example, we used a printSize function, which prints the number of elements (of any type) passed as arguments. It detects the number of elements on compile-time using the sizeof operator. In the case of an empty argument list, the function returns 0.

  • There is a struct defined as Mult, which takes arguments of integer type and return their product. If no argument is passed, it returns 1, which is the neutral element for multiplication.

  • The result is stored in the value, in ...