#include <cstdarg>
#include <cstdio>
#include <iostream>
#include <string>
 
using namespace std;
 
string event(const char* format, ...) {
  va_list length_args;
 
  va_start(length_args, format);
  va_list result_args;
 
  va_copy(result_args, length_args);
  const auto length = vsnprintf(nullptr, 0U, format, length_args);
  string result(length, '\0');
 
  vsprintf(&*begin(result), format, result_args);
  va_end(result_args);
  va_end(length_args);
  return result;
}
 
int main() {
  const auto two = event("%d %d", 13, 42);
  const auto zero = event("lorem ipsum");
 
  cout << two << ' ' << zero << endl;
}

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