Question

#include <stdio.h>
#include <time.h>

int main ()
{
   time_t  time_raw_format;
   struct tm * ptr_time;
   char *buff;
   time ( &time_raw_format);
   ptr_time = localtime ( &time_raw_format );
}

How to copy this to a *buff, return type of ptr_time is struct tm*,my actual goal is to copy system date and time to a char buffer and how to calculate the size returned by localtime, as *ptr_time is a pointer if I do sizeof that i get the value as 4

Answer 1

You can format the time into a char buffer with strftime()

char buff[20];
strftime(buff, sizeof(buf), "%Y-%m-%d %H:%M", ptr_time);

ptr_time is a pointer, *ptr_time is dereferencing a pointer. sizeof(ptr_time) gives the value 4, on a 32 bit system. The size of struct tm is either sizeof(struct tm) or sizeof(*ptr_time), which gives the size of whatever the pointer points to.