What is the meaning of the following C code if output is 0?

[answerhappygod]

#include<stdio.h>
#include<time.h>
int main()
{
struct tm *local;
time_t t;
t=time(NULL);
local=localtime(&t);
printf("%d",local->tm_isdst);
return 0;
}
a) DST is in effect
b) DST status is unknown
c) DST is not in effect
d) DST is corresponding with local time