man pages section 3: Basic Library Functions

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Updated: July 2014



timeradd, timersub, timerclear, timerisset, timercmp - operations on timeval structures


#include <sys/time.h>

void timeradd(struct timeval *a, struct timeval *b,
     struct timeval *res);
void timerclear(struct timeval *tvp);
int timercmp(struct timeval *a, struct timeval *b, CMP);

int timerisset(struct timeval *tvp);
void timersub(struct timeval *a, struct timeval *b,
     struct timeval *res);


These macros are provided for manipulating timeval structures for use with gettimeofday(3C) and settimeofday(3C) operands. The structure is defined in sys/time.h as:

struct timeval {
    long    tv_sec;     /* seconds since Jan. 1, 1970 */
    long    tv_usec;    /* and microseconds */

The timeradd() macro adds the time information stored in a to b and stores the resulting timeval in res. The results are simplified such that the value of res→ tv_usec is always less than 1,000,000 (1 second).

The timersub() macro subtracts the time information stored in b from a and stores the resulting timeval in res.

The timerclear() macro initializes tvp to midnight (0 hour) January 1st, 1970 (the Epoch).

The timerisset() macro returns true if tvp is set to any time value other than the Epoch.

The timercmp() macro compares a to b using the form a CMP b, where CMP is one of <, <=, ==, !=, >=, or >.


These macros are not available in function form. All of these macros evaluate their arguments more than once. If parameters passed to these macros are expressions with side effects, the results are undefined.


See attributes(5) for descriptions of the following attributes:

Interface Stability
MT-Safe with Exceptions

See also

gettimeofday(3C), attributes(5)