Variable number of arguments in C++ [Xcode] - c++

Question

I have a problem with variable number of arguments in C++. I write my code using Xcode.
Here is my code:
#include <iostream>
int sum(int n, ...)
{
int *p = &n;
p++;
int res = 0;
for(int i=0; i<n; i++){
res+=(*p);
p++;
}
return res;
}
int main(int argc, const char * argv[]) {
std::cout << sum(4, 1, 2, 3, 4);
return 0;
}
sum(4, 1, 2, 3, 4) should return a value of 10, but it returns 1606452732.

Answer 1

In C++ you use a template metafunction to do that. It's pretty straight forward:
int sum(int u)
{return u;} // Recursion-End
template<typename... Args>
int sum(int u, Args... rest)
{
return u + sum(rest...);
}
Try it online!
However there is a, as I consider it, depreciated C-way using va_start and va_end. You need to include cstdarg and on function call you need to provide the total parameter count. It would look like this:
int sum(int argnum, ...)
{
va_list arguments;
int i;
int sum = 0;
va_start(arguments, argnum); /* Needs last known character to calculate
the address of the other parameters */
for(i = 0; i < argnum; ++i)
sum += va_arg(arguments, int); /* use next argument */
va_end(arguments);
return sum;
}
Try it online!

Answer 2

From: http://en.cppreference.com/w/cpp/utility/variadic/va_start
#include <iostream>
#include <cstdarg>
int add_nums(int count, ...)
{
int result = 0;
va_list args;
va_start(args, count);
for (int i = 0; i < count; ++i) {
result += va_arg(args, int);
}
va_end(args);
return result;
}
int main()
{
std::cout << add_nums(4, 25, 25, 50, 50) << '\n';
return 0;
}