/usr/man/cat.3/ASN1_TIME_diff.3

ASN1_TIME_set(3)             OpenSSL             ASN1_TIME_set(3)

NAME

     ASN1_TIME_set, ASN1_TIME_adj, ASN1_TIME_check,
     ASN1_TIME_set_string, ASN1_TIME_print, ASN1_TIME_diff -
     ASN.1 Time functions.

SYNOPSIS

      ASN1_TIME *ASN1_TIME_set(ASN1_TIME *s, time_t t);
      ASN1_TIME *ASN1_TIME_adj(ASN1_TIME *s, time_t t,
                               int offset_day, long offset_sec);
      int ASN1_TIME_set_string(ASN1_TIME *s, const char *str);
      int ASN1_TIME_check(const ASN1_TIME *t);
      int ASN1_TIME_print(BIO *b, const ASN1_TIME *s);

      int ASN1_TIME_diff(int *pday, int *psec,
                         const ASN1_TIME *from, const ASN1_TIME *to);

DESCRIPTION

     The function ASN1_TIME_set() sets the ASN1_TIME structure s
     to the time represented by the time_t value t. If s is NULL
     a new ASN1_TIME structure is allocated and returned.

     ASN1_TIME_adj() sets the ASN1_TIME structure s to the time
     represented by the time offset_day and offset_sec after the
     time_t value t.  The values of offset_day or offset_sec can
     be negative to set a time before t. The offset_sec value can
     also exceed the number of seconds in a day. If s is NULL a
     new ASN1_TIME structure is allocated and returned.

     ASN1_TIME_set_string() sets ASN1_TIME structure s to the
     time represented by string str which must be in appropriate
     ASN.1 time format (for example YYMMDDHHMMSSZ or
     YYYYMMDDHHMMSSZ).

     ASN1_TIME_check() checks the syntax of ASN1_TIME structure
     s.

     ASN1_TIME_print() prints out the time s to BIO b in human
     readable format. It will be of the format MMM DD HH:MM:SS
     YYYY [GMT], for example "Feb  3 00:55:52 2015 GMT" it does
     not include a newline. If the time structure has invalid
     format it prints out "Bad time value" and returns an error.

     ASN1_TIME_diff() sets *pday and *psec to the time difference
     between from and to. If to represents a time later than from
     then one or both (depending on the time difference) of *pday
     and *psec will be positive. If to represents a time earlier
     than from then one or both of *pday and *psec will be
     negative. If to and from represent the same time then *pday
     and *psec will both be zero.  If both *pday and *psec are
     non-zero they will always have the same sign. The value of
     *psec will always be less than the number of seconds in a
     day. If from or to is NULL the current time is used.

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ASN1_TIME_set(3)             OpenSSL             ASN1_TIME_set(3)

NOTES

     The ASN1_TIME structure corresponds to the ASN.1 structure
     Time defined in RFC5280 et al. The time setting functions
     obey the rules outlined in RFC5280: if the date can be
     represented by UTCTime it is used, else GeneralizedTime is
     used.

     The ASN1_TIME structure is represented as an ASN1_STRING
     internally and can be freed up using ASN1_STRING_free().

     The ASN1_TIME structure can represent years from 0000 to
     9999 but no attempt is made to correct ancient calendar
     changes (for example from Julian to Gregorian calendars).

     Some applications add offset times directly to a time_t
     value and pass the results to ASN1_TIME_set() (or
     equivalent). This can cause problems as the time_t value can
     overflow on some systems resulting in unexpected results.
     New applications should use ASN1_TIME_adj() instead and pass
     the offset value in the offset_sec and offset_day parameters
     instead of directly manipulating a time_t value.

BUGS

     ASN1_TIME_print() currently does not print out the time
     zone: it either prints out "GMT" or nothing. But all
     certificates complying with RFC5280 et al use GMT anyway.

EXAMPLES

     Set a time structure to one hour after the current time and
     print it out:

      #include <time.h>
      #include <openssl/asn1.h>
      ASN1_TIME *tm;
      time_t t;
      BIO *b;
      t = time(NULL);
      tm = ASN1_TIME_adj(NULL, t, 0, 60 * 60);
      b = BIO_new_fp(stdout, BIO_NOCLOSE);
      ASN1_TIME_print(b, tm);
      ASN1_STRING_free(tm);
      BIO_free(b);

     Determine if one time is later or sooner than the current
     time:

      int day, sec;

      if (!ASN1_TIME_diff(&day, &sec, NULL, to))
             /* Invalid time format */

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ASN1_TIME_set(3)             OpenSSL             ASN1_TIME_set(3)

      if (day > 0 || sec > 0)
        printf("Later\n");
      else if (day < 0 || sec < 0)
        printf("Sooner\n");
      else
        printf("Same\n");

RETURN VALUES

     ASN1_TIME_set() and ASN1_TIME_adj() return a pointer to an
     ASN1_TIME structure or NULL if an error occurred.

     ASN1_TIME_set_string() returns 1 if the time value is
     successfully set and 0 otherwise.

     ASN1_TIME_check() returns 1 if the structure is
     syntactically correct and 0 otherwise.

     ASN1_TIME_print() returns 1 if the time is successfully
     printed out and 0 if an error occurred (I/O error or invalid
     time format).

     ASN1_TIME_diff() returns 1 for sucess and 0 for failure. It
     can fail if the pass ASN1_TIME structure has invalid syntax
     for example.

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See also ASN1_TIME_adj(3)
See also ASN1_TIME_check(3)
See also ASN1_TIME_print(3)
See also ASN1_TIME_set(3)
See also ASN1_TIME_set_string(3)