Directly setting values of struct tm's attributes not working - c++

Question

Why does asctime(ptr) return nothing? All the variables of the struct have values. Can someone explain why does this happen?
I also tried using strftime but the result was the same.
#include <iostream>
#include <ctime>
#include <new>
//#include <cstdio>
using namespace std;
int main(int argc,char *argv[])
{
struct tm *ptr=new struct tm;
//char buf[50];
ptr->tm_hour=0;
ptr->tm_mon=0;
ptr->tm_year=0;
ptr->tm_mday=0;
ptr->tm_sec=0;
ptr->tm_yday=0;
ptr->tm_isdst=0;
ptr->tm_min=0;
ptr->tm_wday=0;
cout << asctime(ptr);
//strftime(buf,sizeof(char)*50,"%D",ptr);
//printf("%s",buf);
return 0;
}

Answer 1

The below program works. Remove zero with 1 and it will work.
struct tm *ptr = new struct tm();
char buf[50];
ptr->tm_hour = 1;
ptr->tm_mon = 1;
ptr->tm_year = 1;
ptr->tm_mday = 1;
ptr->tm_sec = 1;
ptr->tm_yday = 1;
ptr->tm_isdst = 1;
ptr->tm_min = 1;
ptr->tm_wday = 1;
cout << asctime(ptr)
This also works:
ptr->tm_hour = 0;
ptr->tm_mon = 0;
ptr->tm_year = 0;
ptr->tm_mday = 1;
ptr->tm_sec = 0;
ptr->tm_yday = 0;
ptr->tm_isdst = 0;
ptr->tm_min = 0;
ptr->tm_wday = 0;
cout << asctime(ptr);

Answer 2

The behavior of asctime is undefined if any member of struct tm is outside its normal range.
Especially the behavior is undefined if the calendar day is less than 0 (some implementations handle tm_mday==0 as meaning the last day of the preceding month).
Take a look at http://en.cppreference.com/w/cpp/chrono/c/asctime and http://en.cppreference.com/w/cpp/chrono/c/tm for further details.