C ++ is interesting: execute a separate function for each parameter in the Variable Parameter template. The parameter Template

C ++ is interesting: execute a separate function for each parameter in the Variable Parameter template. The parameter Template

For Variable Parameter templates that appear after c ++ 11, we generally process all the parameters in a unified manner. When you need to perform different operations for each parameter or call different functions, the syntax is not directly supported.

Variable Parameter template syntax:

template<typename...T>void function(T...args){}

If you want to execute a function for each parameter indicated by args separately, you can use the following method:

void print(int arg){}template <typename... T>void callfn(void(*fn)(T...args)){    using expand_type = int[];    expand_type{ (print(args), 0)... };}void fn1(int a1, int a2, int a3){}void fn2(int a1, int a2, int a3, int a4, int a5, int a6){}int main(){    callfn(fn1);    callfn(fn2);    return 0;}

In this way, the print function can be called once for each parameter of the function passed in by callfn.

We should first think of using this method.

print(args);...

However, the syntax does not work. Fortunately, we can use the initialization list Syntax:

using expand_type = int[];expand_type{ (print(args), 0)... };

(Print (args), 0) 0 is used to generate a positive number for the brackets, so that the initialization list is legal.

 

Reference 1: https://stackoverflow.com/questions/17339789/how-to-call-a-function-on-all-variadic-template-args