using gmtime() with strftime() (modifying time zone)

Code:

---

// time_convertor.c
// Manilia, Phillipines (15 hrs ahead of San Diego)
// Denver, CO (1 hr ahead of San Diego)

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

#define MDT (-6) // Mountain Daylight Time
#define CCT (+8) // Phillipine Standard Time
#define PDT (-7) // Pacific Daylight Time

void co(void);
void ph(void);

int main(int argc, char *argv[])
{
        time_t now;
        struct tm *ptr;
        char buf1[80];

        printf("Timezone Convertor v0.01\n");

        printf("FLAGS: -co or -ph\n");

        time(&now);

        ptr = localtime(&now);

        strftime(buf1, 80, "%x - %I:%M%p", ptr);
        printf("Pacific Daylight Time : |%s|\n", buf1);

        char str1[] = "-co";
        char str2[] = "-ph";
        int result;
        int result_2;

        result = strcmp(argv[1], str1);

        if(result == 0)
        {
                co();
        }

        result_2 = strcmp(argv[1], str2);

        if(result_2 == 0)
        {
                ph();
        }

        return 0;
}

void co(void)
{
        time_t now;
        struct tm *ptr;

        time(&now);
        ptr = gmtime(&now);

        printf("Denver        : %2d:%02d\n", (ptr->tm_hour+MDT)%24, ptr->tm_min);

        exit(1);
}

void ph(void)
{
        time_t now;
        struct tm *ptr;

        time(&now);
        ptr = gmtime(&now);

        printf("Phillipines : %2d:%02d\n", (ptr->tm_hour+CCT)%24, ptr->tm_min);

        exit(1);
}

---

I was wondering how to use strftime() formatting with these two lines

Code:

---


printf("Denver        : %2d:%02d\n", (ptr->tm_hour+MDT)%24, ptr->tm_min);

printf("Phillipines : %2d:%02d\n", (ptr->tm_hour+CCT)%24, ptr->tm_min);

---

I am even confused. Does this even make sense?

Thanks.

strftime() has a printf feel to it...

This code below will allow you to play with the different formats...

Code:

---

#include <stdio.h>
#include <stdlib.h>

#include <time.h>

int main(void)
{
    time_t timeValue;
    struct tm *tmPointer;

    char timeFormat[0xFF];
    char timeString[0xFF];

    for(;;)
    {
        puts("Enter a strftime() format string or q to quit");

        if((NULL == fgets(timeFormat, sizeof(timeFormat), stdin)) ||
            ('q' == timeFormat[0] && '\n' == timeFormat[1]))
        {
            break;
        }

        timeValue = time(NULL);

        tmPointer = localtime(&timeValue);

        if (0 == strftime(timeString, sizeof(timeString), timeFormat, tmPointer))
        {
            puts("Error - timeString is not big enough");
        }
        else
        {
            printf("Output: %s", timeString);
        }
    }


    return EXIT_SUCCESS;
}

---

strftime() function in C/C++ - GeeksforGeeks
In addition to that list above, there is also
%p - AM/PM
%S - Seconds
%U - Week number (Sunday based)
%w - Weekday (0Sun - 6Sat)
%W - Week number (Monday based)
%X - Full time of day representation
%y - Year without century
%Y - Full year includeing century
%Z - Timezone (or empty if not available)
%% - Single '%' char



Try a few different entries, like this...

%A, %d/%m/%Y, %H:%M:%S %p


Enjoy :)

It's probably best not to use % 24. It doesn't deal with negative values the way you might think (e.g., the result is negative). Also, it won't adjust the day. Instead, use mktime after you've added/subtracted your offset hours. If the hours go below 0 or above 23 it will adjust the values of the struct so that everything is in range. However, you would need to set the tm_isdst member correctly before the call, 1 if daylight savings, 0 if not.