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difftime - calculate time difference
#include <time.h> double difftime(time_t time1, time_t time0);
The difftime() function returns the number of seconds elapsed between time time1 and time time0, represented as a double. Each of the times is specified in calendar time, which means its value is a measurement (in seconds) relative to the Epoch, 1970-01-01 00:00:00 +0000 (UTC).
For an explanation of the terms used in this section, see attributes(7). ┌───────────┬───────────────┬─────────┐ │Interface │ Attribute │ Value │ ├───────────┼───────────────┼─────────┤ │difftime() │ Thread safety │ MT-Safe │ └───────────┴───────────────┴─────────┘
POSIX.1-2001, POSIX.1-2008, C89, C99, SVr4, 4.3BSD.
On a POSIX system, time_t is an arithmetic type, and one could just define #define difftime(t1,t0) (double)(t1 - t0) when the possible overflow in the subtraction is not a concern.
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