struct tm inside another struct - c

Question

I'm trying to calculate the date difference between two dates, using mktime and difftime. One of the dates is a struct tm inside another struct and the other date is a struct tm inside main. mktime works fine one the date inside main, but keeps returning -1 for the date inside the struct. I think I'm overlooking something pretty obvious on how to access a struct inside a struct but I couldn't find the answer. Thanks in advance.

The code is below

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

struct consulta_cand {
    struct tm nascimento;
};

int main(void)
{
    struct consulta_cand candidato;
    time_t now;
    struct tm final2012;
    double timeprint;

    now = time(NULL);
    final2012 = *localtime(&now);
    final2012.tm_mday = 28;
    final2012.tm_mon = 10 - 1;
    final2012.tm_year = 2012 - 1900;
    final2012.tm_hour = 23;
    final2012.tm_min = 59;
    final2012.tm_sec = 59;

    timeprint = mktime(&final2012);
    printf("%.f\n", timeprint);

    candidato.nascimento = *localtime(&now);
    candidato.nascimento.tm_mday = 14;
    candidato.nascimento.tm_mon = 10 - 1;
    candidato.nascimento.tm_year = 1967 - 1900;
    candidato.nascimento.tm_hour = 0;
    candidato.nascimento.tm_min = 0;
    candidato.nascimento.tm_sec = 0;

    timeprint = mktime(&candidato.nascimento);
    printf("%.f\n", timeprint);

    return 0;
}

Which OS are you testing this on? – alk Jun 26 '13 at 16:22 — alk, Jun 26 '13 at 16:22
Windows 7, with TDM-GCC 64-bit – John Blaze Jun 29 '13 at 01:53 — John Blaze, Jun 29 '13 at 01:53

score 0 · Answer 1 · 2013-06-26T16:29:45.860

0

These date functions are based on the epoch year: 1970. You're using a 1967 year.

As an aside: Dennis Ritchie wanted the epoch at 1970 so that the values (both negative and positive) would span his entire life. (Or so he once said in an interview.)

edited Jun 26 '13 at 16:29

answered Jun 26 '13 at 15:57

Thank you, the problem was exactly that. – John Blaze Jun 29 '13 at 01:53

alk · Answer 2 · 2013-06-26T16:21:38.187

0

Are you sure it returns -1, but not simply a negative value, typical -69987600 which are the seconds from 1st January 1970 (back to) 14th October 1967?

That 1967 date is before Epoch time starts, so its Epoch representation is negativ.

edited Jun 26 '13 at 16:21

answered Jun 26 '13 at 16:16

alk

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Yeah, on Windows it was returning -1, when I tried on a *nix box it returned a negative value. – John Blaze Jun 29 '13 at 01:54

score 0 · Accepted Answer · answered Jun 29 '13 at 01:58

0

There is no problem on the way the struct is accessed. The problem is the date before 1970 which mktime() doesn't accept.

answered Jun 29 '13 at 01:58

John Blaze

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struct tm inside another struct - c

3 Answers3