--- title: "Time" canonical_url: https://developer.repebble.com/docs/c/Standard_C/Time/ last_updated: 2026-10-28 sdk_version: 4.33.1 --- # Time Source: https://developer.repebble.com/docs/c/Standard_C/Time/ Standard system time functions This module contains standard time functions and formatters for printing. Note that Pebble now supports both local time and UTC time (including timezones and daylight savings time). Most of these functions are part of the C standard library which is documented at [https://sourceware.org/newlib/libc.html#Timefns](https://sourceware.org/newlib/libc.html#Timefns) ## Function Documentation - [SDK 3](javascript:void(0);) - [SDK 4](javascript:void(0);) - [SDK 4.9+](javascript:void(0);) int strftime(char \* s, [size\_t](https://developer.repebble.com/docs/c/Standard_C/Memory.md#size_t) maxsize, const char \* format, const struct tm \* tm\_p) Format the time value at tm according to fmt and place the result in a buffer s of size max. #### Parameters s A preallocation char array of size max maxsize the size of the array s format a formatting string tm\_p A pointer to a struct tm containing a broken out time value #### Returns The number of bytes placed in the array s, not including the null byte, 0 if the value does not fit. int strftime(char \* s, [size\_t](https://developer.repebble.com/docs/c/Standard_C/Memory.md#size_t) maxsize, const char \* format, const struct tm \* tm\_p) Format the time value at tm according to fmt and place the result in a buffer s of size max. #### Parameters s A preallocation char array of size max maxsize the size of the array s format a formatting string tm\_p A pointer to a struct tm containing a broken out time value #### Returns The number of bytes placed in the array s, not including the null byte, 0 if the value does not fit. [size\_t](https://developer.repebble.com/docs/c/Standard_C/Memory.md#size_t) strftime(char \* s, [size\_t](https://developer.repebble.com/docs/c/Standard_C/Memory.md#size_t) maxsize, const char \* format, const struct tm \* tm\_p) Format the time value at tm according to fmt and place the result in a buffer s of size max. #### Parameters s A preallocation char array of size max maxsize the size of the array s format a formatting string tm\_p A pointer to a struct tm containing a broken out time value #### Returns The number of bytes placed in the array s, not including the null byte, 0 if the value does not fit. struct tm \* localtime(const [time\_t](https://developer.repebble.com/docs/c/Standard_C/Time.md#time_t) \* timep) convert the time value pointed at by clock to a struct tm which contains the time adjusted for the local timezone #### Parameters timep A pointer to an object of type [time\_t](https://developer.repebble.com/docs/c/Standard_C/Time.md#time_t) that contains a time value #### Returns A pointer to a struct tm containing the broken out time value adjusted for the local timezone struct tm \* gmtime(const [time\_t](https://developer.repebble.com/docs/c/Standard_C/Time.md#time_t) \* timep) convert the time value pointed at by clock to a struct tm which contains the time expressed in Coordinated Universal Time (UTC) #### Parameters timep A pointer to an object of type [time\_t](https://developer.repebble.com/docs/c/Standard_C/Time.md#time_t) that contains a time value #### Returns A pointer to a struct tm containing Coordinated Universal Time (UTC) [time\_t](https://developer.repebble.com/docs/c/Standard_C/Time.md#time_t) mktime(struct tm \* tb) convert the broken-down time structure to a timestamp expressed in Coordinated Universal Time (UTC) #### Parameters tb A pointer to an object of type tm that contains broken-down time #### Returns The number of seconds since epoch, January 1st 1970 [time\_t](https://developer.repebble.com/docs/c/Standard_C/Time.md#time_t) time([time\_t](https://developer.repebble.com/docs/c/Standard_C/Time.md#time_t) \* tloc) Obtain the number of seconds since epoch. Note that the epoch is not adjusted for Timezones and Daylight Savings. #### Parameters tloc Optionally points to an address of a [time\_t](https://developer.repebble.com/docs/c/Standard_C/Time.md#time_t) variable to store the time in. If you only want to use the return value, you may pass NULL into tloc instead #### Returns The number of seconds since epoch, January 1st 1970 double difftime([time\_t](https://developer.repebble.com/docs/c/Standard_C/Time.md#time_t) end, [time\_t](https://developer.repebble.com/docs/c/Standard_C/Time.md#time_t) beginning) Obtain the number of seconds elapsed between beginning and end represented as a double. ##### Note Pebble uses software floating point emulation. Including this function which returns a double will significantly increase the size of your binary. We recommend directly subtracting both timestamps to calculate a time difference. ``` int difference = ts1 - ts2; ``` #### Parameters end A [time\_t](https://developer.repebble.com/docs/c/Standard_C/Time.md#time_t) variable representing some number of seconds since epoch, January 1st 1970 beginning A [time\_t](https://developer.repebble.com/docs/c/Standard_C/Time.md#time_t) variable representing some number of seconds since epoch, January 1st 1970. Note that end should be greater than beginning, but this is not enforced. #### Returns The number of seconds elapsed between beginning and end. - [SDK 3](javascript:void(0);) - [SDK 4](javascript:void(0);) - [SDK 4.9+](javascript:void(0);) [uint16\_t](https://developer.repebble.com/docs/c/Standard_C.md#uint16_t) time\_ms([time\_t](https://developer.repebble.com/docs/c/Standard_C/Time.md#time_t) \* t\_utc, [uint16\_t](https://developer.repebble.com/docs/c/Standard_C.md#uint16_t) \* out\_ms) Obtain the number of seconds and milliseconds part since the epoch. This is a non-standard C function provided for convenience. #### Parameters tloc Optionally points to an address of a [time\_t](https://developer.repebble.com/docs/c/Standard_C/Time.md#time_t) variable to store the time in. You may pass NULL into tloc if you don't need a [time\_t](https://developer.repebble.com/docs/c/Standard_C/Time.md#time_t) variable to be set with the seconds since the epoch out\_ms Optionally points to an address of a [uint16\_t](https://developer.repebble.com/docs/c/Standard_C.md#uint16_t) variable to store the number of milliseconds since the last second in. If you only want to use the return value, you may pass NULL into out\_ms instead #### Returns The number of milliseconds since the last second [uint16\_t](https://developer.repebble.com/docs/c/Standard_C.md#uint16_t) time\_ms([time\_t](https://developer.repebble.com/docs/c/Standard_C/Time.md#time_t) \* t\_utc, [uint16\_t](https://developer.repebble.com/docs/c/Standard_C.md#uint16_t) \* out\_ms) Obtain the number of seconds and milliseconds part since the epoch. This is a non-standard C function provided for convenience. #### Parameters tloc Optionally points to an address of a [time\_t](https://developer.repebble.com/docs/c/Standard_C/Time.md#time_t) variable to store the time in. You may pass NULL into tloc if you don't need a [time\_t](https://developer.repebble.com/docs/c/Standard_C/Time.md#time_t) variable to be set with the seconds since the epoch out\_ms Optionally points to an address of a [uint16\_t](https://developer.repebble.com/docs/c/Standard_C.md#uint16_t) variable to store the number of milliseconds since the last second in. If you only want to use the return value, you may pass NULL into out\_ms instead #### Returns The number of milliseconds since the last second [uint16\_t](https://developer.repebble.com/docs/c/Standard_C.md#uint16_t) time\_ms([time\_t](https://developer.repebble.com/docs/c/Standard_C/Time.md#time_t) \* tloc, [uint16\_t](https://developer.repebble.com/docs/c/Standard_C.md#uint16_t) \* out\_ms) Obtain the number of seconds and milliseconds part since the epoch. This is a non-standard C function provided for convenience. #### Parameters tloc if provided receives the current UTC Unix Time seconds portion out\_ms if provided receives the current Unix Time milliseconds portion #### Returns Current Unix Time milliseconds portion [time\_t](https://developer.repebble.com/docs/c/Standard_C/Time.md#time_t) time\_start\_of\_today(void) Return the UTC time that corresponds to the start of today (midnight). #### Returns the UTC time corresponding to the start of today (midnight) ## Typedef Documentation typedef unsigned int time\_t time in seconds since the epoch, January 1st 1970 ## Macro Definition Documentation #define TZ\_LEN 6 #define SECONDS\_PER\_MINUTE (60) #define MINUTES\_PER\_HOUR (60) #define SECONDS\_PER\_HOUR (SECONDS\_PER\_MINUTE \* MINUTES\_PER\_HOUR) #define HOURS\_PER\_DAY (24) #define MINUTES\_PER\_DAY (HOURS\_PER\_DAY \* MINUTES\_PER\_HOUR) #define SECONDS\_PER\_DAY (MINUTES\_PER\_DAY \* SECONDS\_PER\_MINUTE)